To change the color, you have to go on the "Material menu" below.
click on "new" to create a new material.
Then, you can change several parameters:
- diffuse is the color of the object / just click on the color to change the RGB values
- specular is about how the light is reflected by the object
- shading is how much glossy the object is
I guess, you are using the default rendering system which is "Blender Render". The ultimate level is the "Cycle Render" which uses the "Nodes" but quite complex to explain in few minutes ... I'm sometimes lost in the settings but so many possibilities ... maybe too much complex for a watchface ...