You can tint TotalBoat Halcyon with a low percentage of mica powder, from .5-2%, to create a custom color. We don't recommend using other types of tints, inks, or pigments because these could compromise the performance of the varnish.
Halcyon is a water-based varnish, so if you still want to attempt tinting it, do a small test sample, and only use tints that are water based, or tints that are compatible with water-based finishes. Typical safe amounts of tints will be from .5-2%. The purpose of a small test is to ensure that the tinted Halcyon adheres well, cures properly, and develops the characteristic hardness.