necropunk

Chilly, I have never considered that and will be wholeheartedly stealing the idea, thank you. I'm not sure about making tiles for every color all at once, but definitely for my next few colors I'll be trying that out. 

Some folks make a color pallet painting a stripe of all their underglazes then covering 1/2 with their clear glaze and fire to cone so they have a reference with how each underglaze changes with a specific glaze applied over top at a specific cone. One big test tile, many colors, one, two, and three coats half covered with your favorite clear.
Amaco and Mayco also have samples already made and there are sites that have examples. One such: https://www.thestudiomanager.com/
 

I'ld try a heavier application of the underglaze. Let each coat dry before putting on the next and brush each coat in the opposite direction to the last to get good even coverage.  Good to see you are trying them on test tiles, try a few with different glaze thicknesses and see what you get.