The simple answer is
But ... it can be a bit more than that to change a color
1.) Be sure, as you stated
, that the two components are truly fully compatible - this includes checking the Data Sheet(s) for differences in mix ratio/reducer/diluent(solvent)/activator, substrate requirements, open coat/re-coat specs, top-coat requirements and others can be different even in 'like' product lines.
2.) It takes "a ton" of a lighter pigment to 'move' a dark color to a lighter shade.
You don't want to take the entire amount of the 'dark' you have and start adding the 'light' in trying to achieve a color you want/like.
It is best to make several small test mixes with varied ratios to test for the actual color you like - even then, you may not have enough of the 'lighter' color to actually move the darker color to the shade you like.
So - see #3 ...
3.) Call the paint supplier you worked with and ask them if they will tint the darker color for you to get what you'd like.
Most good suppliers will work with me to move an already purchased color a shade or two to get a color that better fits my needs.
And the min. they will give/sell me a tinting mixture to do the work myself if I'm not sure of the exact 'move' I need for a given vehicle/match/like.
Hopefully one of the 'full-timers' will chime-in also
(ps: I'll be cruising back through your town in a few days on 84 - I'll be the one in the Bronze Trailblazer ... with a pistol, but without a hat ...