I am red green color blind and I have a real hard time with the colors used for the preview.
The items tends to look like a giant blob for me because the color of green all blends together.
An excellent enhancement would be to allow the user to choose what color is used for the preview, and optimally a different color for the current layer or line.
I typically use the layer selection in the preview, so if I could choose blue for my main model color and an orange for the current layer as selected by the end slider.