So I had to re-template my Expedition that I have been working on and used it a chance to try and make a guide on how I make my "rainbow' templates.
I'll let it be noted I am not the best at giving instructions and I have a strong studder but this should help somewhat.
You don't need to remove the white color to add the mesh to the rainbow template.
Just open the rainbow template, create a new layer, add a white template with a mesh there, double click on a that layer and select "mix - multiply"
This way the layers will blend, there will be no white color, and the mesh will perfectly fit on the layer with the rainbow template.
It will look better, plus it is faster and easier to do.