You need to use the group tool first, to select the polygons of the area you want to change colour. Then press the 'add material' button to create a separate material group for that selection. now you can go into the Material room and change the diffuse colour for that group.

Another way to do this would be to use a blender map. If your texturing and 2D skills are up to it, then create a black and white map in Photoshop/Paintshop Pro/GIMP/your preferred image editor, painting the scapula area in white and the rest in black. Now, in the body/torso/relevant material of your figure, use a blender node. Set colour 1 to white, and input in the original skin's texture map. Make the second colour red. Set the Blending parameter to 1, and plug in the black and white map you created. This will colour the scapula region red, and keep the original texture for the rest of your figure. It's a useful trick to use if the area yo want painted contains fine details, or does not correspond exactly to polygon shapes (which is most often the case).

Using control maps like this can be used for a multitude of effects, from controling the ambience, specularity, bump, displacement, and transparency of a material.

Hope this helps.

jonthecelt