painting without an airbrush

hello fellow cakers!!

i am trying to figure out the best efficient way to undertake a super mario themed birthday cake for my twin boys. i wanted to do a small 3 tiered cake and do two different scenes on the bottom to tiers and then make a red piranha plant coming out of a pipe for the top tier. i’m doing a scene from the classic mario on the bottom and on the middle i wanted to do a scene from the new super mario bros wii. this is the scene from the new one (sorry i can’t figure out how to paste it directly on here):

http://ve3d.ign.com/articles/news/game/14354229/Wii/New-Super-Mario-Bros-Wii

it’s the first scene shown. so my question is: a lot of the “hills” appear in the background and i wanted to paint them on, but i don’t think that it would look good if i cover the whole thing in blue fondant. i don’t have an airbrush right now and was thinking about using a very light blue fondant and then painting the sky a darker blue and then painting the hills on. that way the coloring wouldn’t be that off when i paint the hills right on. What it’s the best way to paint the sky?

thanks so much for your tips and advice!