What type of effects are categorized as layer 1?

Layer 1 in the comprehensive rules of Magic: The Gathering is specifically concerned with the characteristics of a permanent that are defined independently from its abilities. This includes effects that affect who controls the permanent. Control-changing effects fall under this category because they alter the controller of the card without modifying its inherent characteristics such as color or abilities.

Control-changing effects are the first type of effect applied in the game as they directly define who has ownership of a particular permanent, anchoring the permanent's existence within the game state.

The other choices deal with different types of effects. Color-changing effects, which belong to layer 6, change what color a permanent is, while ability-adding effects fit into layer 2, as they grant or remove abilities from permanents. Lastly, stating "All effects applied to cards" would mistakenly suggest that all types of game effects operate within layer 1, which is not the case. Each layer has a specific function according to the rules, and only control-changing effects belong in layer 1.