Yay! I just ordered Royal Blue yesterday, glad to see you posted that
Do you prime yoyr Frenchies white or black?
With white as a base, the R.Blue may seem too light, in fact prussian blue would be better as regards the light/dark factor. But R. Blue seems to me more accurate regarding the shade. SO, by using R.Blue on white, u either mix it with a bit of black, OR, try to darken things over with oil paint later on.