Well officers could wear what they liked within reason and regulations. Artwork shows some officers in blue patrol jackets and such, but I haven't seen any photos showing this, so that could be artistic licence. The problem with khaki uniforms being worn by officers commanding men in the grey serge is that they probably wouldn't own a khaki uniform, unless they had taken the trouble to have one made privately. It was the first time most of those units wore anything other than British scarlet.
There is a group photo of officers of the Adjutant General's and Quatermaster General's departments at Suakin in 1885. They are all are in khaki/grey uniform worn on that campaign except one, who is still in a scarlet jacket (with tartan trews). So I don't think it is entirely outside the bounds of possibility to have the odd fellow here and there ignoring the general orders for campaign dress, if you want to mix things up a bit.