Flat Red and Hull Red

I always get nervous about mixing up custom colors for very visible parts. It is nearly impossible to create an identical batch if some touchup is needed later and I don't have any of the original batch left. Red would be especially problematic to match, IMHO. If I were in your place, I'd use a ready-mixed color anyway.

My guesstimate is that you would get a deeper, darker red, with a hint of brown to it. Something like a primer red or red oxide shade. Or a USN type of Hull Red ;-)

I find British Crimson to be an excellent representation of the anti-fouling paints used on seagoing ships.  Iron oxide primer makes a good representation (is actually the same paint) as often used on freshwater ships.

The color I was trying to find out is for the oil tanks located on the front landing gears of the Mossie. Last night, I did a search on the color and found it. Stik is right. It is a red oxide shade type of color.