The neat thing is with this image I taught myself to use blends to simplify the use of gradients in illustrator.

Basically, create a clipping mask of the area you are coloring. Lay down the base color of the area, filling in the whole shape. On top ofthat lay down a containment shape that is of the same color as thebase. This should probably be an approximation of the overall perceivedshape of the blended area but can be adjusted afterwards. Then lay downa smaller shape in the desired blending color. Select both and hitALT+CTRL+B to create the blend. If you haven't already move theclipping mask shape above the rest of the group select all members ofthis group and hit CTRL+7 to clip the extra areas. If needed you canadjust any of the shapes to resize/reshape the blend area (i.e. theshape of the blend would be controlled mostly by the containing shapewhile the intensity of the color by the size/shape of the blend colorshape) which can still be adjusted after making the blend. Also thereare probably proper terms for this but I'm just making names up on thefly so please don't consider this a real tutorial.