I use Tamiya paints for my roundels.   Roundel red is XF-7 Flat Red and XF-9 Hull Red 75:25   Blue is XF-8 Flat Blue, XF-17 Sea Blue and XF-1 Flat Black. The ratio is approximately 75:15:10 I think. I sometimes use semi gloss black instead so it's not as flat.   Yellow is XF-3 Flat Yellow and a drop of XF-7 Flat Red   Hope that helps.   Carl