I know what you mean about the colored coded +12v rails on most Dells, but these I'm working with now don't list colors on the
They don't list the color codes, you just have to look at known 12V connectors, or 12V.pins on connectors to see which is which.
If you do the math you'll find that each 18A.x 12V. rail is 216W. That's why the 375W PSU from the T3400 has the same 2x18A rails as the Optiplex 305W. but adds a 75W GPU cable ( on the white rail). The optional 425W has a 3rd 18A. rail and adds another 75W GPU cable. The 525W. from the T35000 adds an 8 pin CPU connector but just 1 GPU cable on the same 3x18A rails. That's also where they start with replaceable harnesses.
https://www.hardwareinsights.com/dell-h305p-01-power-supply-review/