The decisions made before anyone picks a colour
Design is not decoration applied at the end. By the time somebody is choosing colours, the decisions that determine whether the thing is usable have already been made — in the flow, the wording and the order of the steps.
We do that earlier work: watching people use what exists, finding where they hesitate, and testing a prototype before it is expensive to change. The measure is not whether it looks current in two years. It is whether support calls go down.