How to mix Norrells tan flat to match KAC SR15 FDE color

[Lawdog-1]

I want to use Norrells Moly-resign Tan Flat and do need to add a little Brown Flat and or add a little Red Flat to try to match KAC FDE/Taupe SR15/SR25 gun color?

[TehLlama]

un-PC answer - paint it all a new version of FDE?
The Taupe looks like a tiny bit ofr the Brown Flat mixed in, but it may take you a couple swatches on some stray parts to check how close the match is.
Might be worth doing an inventory or random unused parts, paint those, judge off it, and if you were planning on selling those off, you still might be money ahead.