Thanks so much! They aren't that hard, actually, at least not digitally. The trick here was to work with a light colour against a dark background and set the brush to a low opacity so I could gradually build up the colour and light. :)
Oh, yeah, painting with a mouse is tough!! Traditionally I'd say... try pastels or chalk on black or dark-coloured paper? I drew a fairy like that once and it worked pretty well. Oil paint would work too, but that's messy and takes ages. Oil pastels, though... or prismacolor pencils if you can get them.