i've been playing around with SumoPaint (it's browser-based) on my Chromebook and i've had fun with it. i've also been using Sketch (mac), though it seems more geared towards vector work (i use it for a lot of UI work...)

Another cheap (inexpensive) alt is Pixelmator (mac/iPad) - (sorry for the MAC alternative as that's my work platform of choice ;) )  

It really depends on WHAT you want to do ... if it's more for color-correction, that's one thing, for creating textures is another...

scott