What color pearl did u mix into the clear? If it was a white pearl, then that explains the color change of the base coat, but not the “dullness” of the clearcoating.
A Blue car with a white or silver pearl wil lighten in color; just by the nature of pearl; Thus pearls work best on Black or White cars when using odd-ball pearls. If you are using a colored pearl onto color (Green on Blue or etc) then there will some color shift of the base color due to the pearl as well; but no real lightening effect of a white pearl.
Bottom line is this, Pearl does shift color pretty much no matter what; thus some of what you are seeing is expected, some I believe is an issue with the clear and harderner/reducer.