Match the use-case: for sandwiches/quesadillas pick a blend (Monterey + cheddar or cheddar + mozzarella) for Colby Jack’s balance.
For baking (casseroles, mac-style bakes), choose cheddar-forward options if you want more browning; choose Monterey-forward options if you want a smoother top.
Use the listed ratio (typically 1:1 by weight); for blends, measure each cheese separately, then mix.
If your substitute melts but looks too oily, lower heat or shorten bake time; if it’s not browning, bake a bit longer or broil briefly.
Taste after melting: add a tiny pinch of salt or a squeeze of lemon only if your cheese tastes flat compared to Colby Jack.