To be convincing, you need to be aware of the following:
- Your shadows should be warm.
Your deepest cast shadows should be warmer than ordinary shadow (even "hot").
Make your halftones cool, but keep the value light. This cool halftone separates your warm light from your warm shadow area.
Always keep your areas of light warm.
And in those areas of light, your highlights can be slightly cooler than the light surrounding it.
Here's another "key to reality painting": Keep your red tones concentrated between the eyebrows and the chin. Avoid the use of red on the neck and forehead.