Board Game Arena

While I agree that it would be ideal to be able to distinguish everything at a glance, it's an Anglocentric approach to the problem. The advantage of tooltips is that they can be localized. Roughly half the game's players hail from non-English-speaking countries. Relying on tooltips may not be ideal for you, but it is the ideal solution for the other half of the world.

Is it correct to say that a hybrid technology only needs one prerequisite that matches one of its colors, so if a tech has blue and yellow half-triangles on its left, and the 2 techs leading to its position have yellow and red triangles on their right ends, then the tech can be placed?

The player who researches chooses which color from the triangles on the right side of the prerequisites. If the researcher chose yellow, the yellow/blue card would be eligible.