Yes. Any type of color, hue, saturation, etc. adjustments that are made to the entire image are permitted in Basic Editing.
...in normal mode.
Therefore, I don't think an action like digidaan's b&w conversion is acceptable in basic editing challenges.
Someone want to help me to verify that?
I know there is a thread on it somewhere, but....
DigiDan's technique makes use of two layers, one that blends in color mode and another in normal mode.
According to the Basic Editing Rules, this does look to be prohibited as you suggest.
Layers: Only adjustment layers may be used, and the layer must be applied in normal mode. All other types of layers and all other blending methods (modes) are prohibited. Layers may not be used to apply a prohibited effect to an image.
