Approaches for encoding or decoding when switching color spaces involve signaling of control information for adaptive color space transformation (“ACT”). For example, an encoder encodes a unit of video to produce encoded data. As part of the encoding, the encoder evaluates a condition for the unit and conditionally signals a syntax element that indicates whether ACT is enabled within the unit. The encoder outputs the encoded data as part of a bitstream. A corresponding decoder receives encoded data as part of a bitstream. The decoder decodes the encoded data to reconstruct a unit of video. As part of the decoding, the decoder evaluates a condition for the unit and conditionally parses a syntax element that indicates whether ACT is enabled within the unit. The syntax element is parsed if the condition is satisfied, but otherwise the parsing of the syntax element is skipped.