Paintbrush isn't my favourite tool by any means Kaz.  My biggest problem with it apart from the lack of size control response to pressure is how quickly it runs out of paint too, no matter how long you try and make the tail off.  I do tend to do as BJ suggested and have it thinned out a fair bit, as and when I do have a go with it.

More often I stick with the pencil, chalks and felt tips, working back into them with the palette knife.  The paintbrush is handy for blocking in colour early on.  If I get any results worth looking at it's more by bloody mindedness than talent. 

Much as I'd love to have you visit Gloucester one day, I'd prefer you weren't heavily armed with anything more powerful than good wine.  Perhaps I should insist on a plastic bottle that's more effort to beat me to death with as well

ok well i'm having another go at it, i'll leave the paintbrush well alone i think! 

so i'm trying to paint a dress, it's orange & i thought i'd have a go with the felt pens, but no matter where i move the colour to on the slider/colour wheel, the pen is painting brownish? i've dropped all the settings & tried different settings, but no use, if i move the slider to metallic, it's a slightly less saturated brown.

Do the pens behave like that? erm help again please!!

i'm coming to Gloucester! will vodka in a plastic bottle do Nick?  

There's 2 sections to the colour picker. There's the big area where you select a colour, then there's a strip along side that which adjusts the value. Do you have that slid down toward the bottom?

Or, have you got that layer set to a blending mode other than normal that could be affecting the colour?

i've done a screen grab to show you the colour it's painting with the settings i have. 

I can't get it to do the same with mine. All I can think is that you have a blending mode set for that layer. I tried all the modes too and still couldn't get that.

Does one of the layers below it have a blend mode set?

ok, i've just opened a new canvas & clicked reset tool for the felt pens, the blend is normal, i haven't changed any settings & it's still the same, do you think like pix says it's because of the metallic slider thing? 

 *edit* yeah it is the metal slider, i'm sure it was full to the left before! urgh, well that's what the problem was then, so what's the point of that? it's like multiply?