I've seen this a popular go to mix using Tamya acrylics:
Dull Roundel Red – Mix of 75% flat Red (XF-7 ), 25% NATO Brown (XF-68)
Blue – Mix of 95% flat Blue (XF-8), 5% flat Black (XF-1)
Yellow – Flat Yellow (XF-3) with a tiny amount of flat Red (XF-7)
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Don't have a 1/32 scal Spit, but looking at one in 1/48, I can see where the decal problem would arise. Sometimes even liberal amounts of softening fluid wll not help, and you can do the option of masks, or just cut out the problem section and fill the required area with paint - problem now is matching the decal colours.
regards,
Jack