Try in Amphibian Biology (Heatwold H & Barthalmus GT, eds), Vol. 1, Surrey Beatty & Sons, Chipping Norton, NSW, Australia
You can review the discussion in there as well as the references.
Yes amphibians can convert other pigment cells to melanopores under stimulation. This can even occur in dietary supplementation. Axolotls for example can be made melanistic through the addition of excess allopurinol into the diet. Excess stimulation of the melanocytes can cause the conversion.
A phrase you never want to hear;
"It seemed like a good idea at the time."