I've recently begun doing some painting again (my Imperial Gua...Astra Militarum *sigh*) and have been trying to do them a bit more properly this time around (still not at a high quality, but at as high as I am going to get!).

So, I am painting them using a wet palette and doing multiple layers rather than simply glopping a single layer on. This works, for the most part, well. But I have hit a snag. When I accidentally get paint that goes on one painted part of the model that it shouldn't do, I am struggling to correct the issue because the watered down paint that I then reapply doesn't cover the mistake entirely (due to it being watered down).

To give an example: My guard have a red and white color scheme, with black and metal used for weapons and pouches etc. I have been painting the red first, then doing the white. Occasionally minor specks of white get onto the red or areas of white edge over into red allocated zones. When I try to correct this, the watered down correction color does not cover the mistaken paint entirely (as its watered down). How can I correct this? Should i use thicker unwatered paint for doing corrections, or what should I do?

Any tips much appreciated.

If you're really speedy you can sometimes clean up mistakes as they happen with a clean, dry brush. Otherwise I'd say maybe use a thicker version of whatever the base colour is to do your touch ups.

I'm having similar issues, but find they only really happen around edges where it gets fiddily. I'm painting 1:1 water:paint on most areas, but then 1:4 around edges as a clean up and that is thick enough to deal with the specks. That said I'm painting in very dark tones, so likely easier to fix than a black speck on white.

I second what Scythe said a quick clean dry or damp brush before the paint sets. Another alternative I have used a sharp scalpel blade to scrap it off.