DIMM slot 1 is 3, 3 is 1, 2 is 4. I'm running 4x8gb ddr4 Corsair Vengeance RGB Pros on a Asus crosshair VII Hero board on windows 10. I found this issue when I tried to use iCue to change the coloring on the sticks, only to find out that they're in the wrong order somehow.
As I know, Single Rank DIMM is more expensive than Dual Rank DIMM. In order to pack the same amount of memory on Single Rank DIMM, the manufacturers have to use bigger capacity chips to make up for it. That's why Single Rank DIMM tends to be more expensive. I believe Rank has something to do with the number of connectors to the Chips on a DIMM.

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The different colors of your dimms have nothing to do with what type of ram your board will accept or use. Each MB manufacturer use the color they do for aesthetics only. The reason they are two. Each channel has DIMM 0 and DIMM 1. Manual says something to effect: place MATCHING ram modules in Channel A DIMM 0 and Channel B DIMM 0. There is also entry for when using nonmatching ram modules. The manual tells me what to install where. Do I need colors to follow instructions in the manual? Do I need the actual slots color coded?

Memory Channels

In the fields of digital electronics and computer hardware, multi-channel memory architecture is a technology that increases the data transfer rate between the DRAM memory and the memory controller by adding more channels of communication between them. Theoretically this multiplies the data rate by exactly the number of channels present. Dual-channel memory employs two channels.

Single-channel (asymmetric) mode
This mode provides single-channel bandwidth operations and is used when only one DIMM is installed or when the memory capacities of more than one DIMM are unequal. When using different speed DIMMs between channels, the slowest memory timing is also used.

Single Channel memory, with a maximum rated clock of 400 MHz and a 64-bit (8 bytes) data bus is now becoming obsolete and is not being produced in massive quantities. Technology is adopting new ways to achieve faster speeds/data rates for RAM memories.

Dual-channel architecture

Dual channel memory slots, color-coded orange and yellow for this particular motherboard.

Dual-channel-enabled memory controllers in a PC system architecture utilize two 64-bit data channels. Dual channel should not be confused with double data rate (DDR), in which data exchange happens twice per DRAM clock. The two technologies are independent of each other and many motherboards use both, by using DDR memory in a dual-channel configuration.

Dual-channel

architecture requires a dual-channel-capable motherboard and two or more DDR, DDR2 SDRAM, or DDR3 SDRAM memory modules. The memory modules are installed into matching banks, which are usually color-coded on the motherboard. These separate channels allow the memory controller access to each memory module. It is not required that identical modules be used (if motherboard supports it), but this is often recommended for best dual-channel operation.

Motherboards supporting dual-channel memory layouts typically have color-coded DIMM sockets. Coloring schemes are not standardized and have opposing meanings, depending on the motherboard manufacturer's intentions and actual motherboard design. Matching colors may either indicate that the sockets belong to the same channel (meaning that DIMM pairs should be installed to differently colored sockets), or they may be used to indicate that DIMM pairs should be installed to the same color (meaning that each socket of the same color belongs to a different channel). The motherboard's manual will provide an explanation of how to install memory for that particular unit. A matched pair of memory modules may usually be placed in the first bank of each channel, and a different-capacity pair of modules in the second bank.^[6]

Modules rated at different speeds can be run in dual-channel mode, although the motherboard will then run all memory modules at the speed of the slowest module. Some motherboards, however, have compatibility issues with certain brands or models of memory when attempting to use them in dual-channel mode. For this reason, it is generally advised to use identical pairs of memory modules, which is why most memory manufacturers now sell 'kits' of matched-pair DIMMs. Several motherboard manufacturers only support configurations where a 'matched pair' of modules are used. A matching pair needs to match in:

Capacity (e.g. 1024 MiB). Certain Intel chipsets support different capacity chips in what they call Flex Mode: the capacity that can be matched is run in dual-channel, while the remainder runs in single-channel.
Speed (e.g. PC5300). If speed is not the same, the lower speed of the two modules will be used. Likewise, the higher latency of the two modules will be used.
Same CAS Latency (CL) or Column Address Strobe.
Number of chips and sides (e.g. two sides with four chips on each side).
Matching size of rows and columns.

Dual-channel architecture is a technology implemented on motherboards by the motherboard manufacturer and does not apply to memory modules. Theoretically any matched pair of memory modules may be used in either single- or dual-channel operation, provided the motherboard supports this architecture.

Performance

Theoretically, dual-channel configurations double the memory bandwidth when compared to single-channel configurations. This should not be confused with double data rate (DDR) memory, which doubles the usage of DRAM bus by transferring data both on the rising and falling edges of the memory bus clock signals.

Tom's Hardware found little significant difference between single-channel and dual-channel configurations in synthetic and gaming benchmarks (using a 'modern (2007)' system setup). In its tests, dual channel gave at best a 5% speed increase in memory-intensive tasks.^[7] Another comparison by Laptop logic resulted in a similar conclusion for integrated graphics.^[8] The test results published by Tom's Hardware had a discrete graphics comparison.

Another benchmark performed by TweakTown, using SiSoftware Sandra, measured around 70% increase in performance of a quadruple-channel configuration, when compared to a dual-channel configuration.^[9]^{:p. 5} Other tests performed by TweakTown on the same subject shown no significant differences in performance, leading to a conclusion that not all benchmark software is up to the task of exploiting increased parallelism offered by the multi-channel memory configurations.^[9]^{:p. 6}

Ganged versus unganged

Dual-channel was originally conceived as a way to maximize memory throughput by combining two 64-bit buses into a single 128-bit bus. This is retrospectively called the 'ganged' mode. However, due to lackluster performance gains in consumer applications,^[10] more modern implementations of dual-channel use the 'unganged' mode by default, which maintains two 64-bit memory buses but allows independent access to each channel, in support of multithreading with multi-core processors.^[11]^[12]

'Ganged' versus 'unganged' difference could also be envisioned as an analogy with the way RAID 0 works, when compared to JBOD.^[13] With RAID 0 (which equals to 'ganged' mode), it is up to the additional logic layer to provide better (ideally even) usage of all available hardware units (storage devices, or memory modules) and increased overall performance. On the other hand, with JBOD (which equals to 'unganged' mode) it is relied on the statistical usage patterns to ensure increased overall performance through even usage of all available hardware units.^[11]^[12]<

Why Are Dimm Slots Different Colors