Lets say we want Kida to be ascending in a Purple light instead of Blue... first, press Ctrl-L to open the Layers window and duplicate the layer

Now we colourize the top layer, by going Image>Layer>Colours>Colourize

A new window will appear that looks like this

This really requires your experimenting skills now, because the numbers will differ for each picture! It's also a matter of preference and what you want for your picture. For this one however, I used Hue=289, Saturation=82, and Lightness=30. Click the good old OK Button and you'll have your different colour!

Now, sometimes you might want to leave it like that, but you have many other options now! We're going to erase some of the top layer so we have only some purple and some blue! Now you need to decide what you want blue in the picture... I've decided that I'm going to make Blue again! There are several different ways to select the part you're going to erase, like the rectangular for squares, which you won't find often, the lasso selector, or if you like free style, the eraser without selecting. I'm select the Eraser tool because it will be more work to select all the way around Kida. To make this easier yet, I'm going to zoom in majorly (Image>View>Zoom>400%), then I can select it easier. Remember, the size of your brush can be reduced! If it's huge you're going to have a heck of a time erasing anything! To help you see what exactly you're turning blue, you may want to hide the top layer (Ctrl-L - Click the eye on the layer you want to hide). Well after much erasing, this is my finished product