Restoration of old organ

I am restoring an old pipe organ. This organ is made of Mahogany, some dark and yellow/brown veneers. While i can match the dark colours, other than stain on light veneers, what is the best way of yellowing veneers to match the original? I will be polishing the veneers with shellac. Any advice will be appreciated.

We need pictures of what your trying to match and the timber types. And include a picture of the whole piece not just a close up shot of the wood.