Looks like you're really working on this digital colouring technique, MMM

The sea is just a tad over-saturated for my personal taste but the map as a whole is a good practice piece.

If you don't mind, I have a few tips that might help with your next exercise:

Put the scanned map image at the top of the layer stack and make it transparent by changing the layer mode to multiply. Then find a nice subtle parchment to put right at the bottom of the stack to act as the background for your colours, which will then be on all the layers between those two main layers - the background parchment and the scanned map.

With the layers between - the colour layers, don't try to paint transparently with a transparent brush (which is always nearly impossible to get right), but paint in good solid colour - full opacity, and use the layer transparency itself to set the transparency of your colour washes. Also try a few different blend modes on those colour layers, like overlay, multiply and grain merge, etc which may help. Its a lot easier to paint with an opaque brush in solid colour and use the qualities of the layer you are painting on to give transparency and blend effects