I've mainly use deionised water since it can be bought for cheap, and then add a couple drops of concentrate if i wanted colour.
Touchwood, never had issues even when not using biocide (i have never tried.. just pure water), but thats subjective. I tend to flush my loop every couple years and not had any troubles.
I am a bit mixed with cryofuel. I am still testing what i like (may just stick with ol fashioned deionised), but i also have Azure Blue, normal blue, Mystic Fog and Cloud White.. all unopened apart from Mystic white... may have just been me, but the Mystic started separating after a month of use and staining the reservoir and blocks etc, so that kinda put me off.
In that case, i believe using pastel colours is only ideal for show builds as a temporary, but for long term to stick with vanilla water and add your own dye if needed.