True "Candy Apple" colors are a two-part paint. I don't know if CP uses real Candy Apple red, as it would be pretty expensive.
For a real Candy Apple Red, a translucent red topcoat would be applied over a metallic undercoat. Most Candy Reds are translucent red applied over a gold basecoat. This allows light to penetrate the red, be reflected off the gold, and pass again through the red. Different effects can be made by using different undercoats: gold, silver, copper. Copper would give a warmer color than gold; silver would give a cooler effect.
Candy topcoats are available in a variety of colors: red, blue, green, orange, purple.
To do this on a locomotive would double both the paint cost and the labor cost.