Regimental colours weren't carried in the field by the time of the Sudan campaigns (IIRC Laing's Nek 1881 was the last time). I guess there might have been the odd Union Flag in use, and I think that General Graham used a plain red flag to mark his command post.
Having said that, if you want Colour Parties for 1883-5 (I know I did), use the 1879 (Zulu War) ones available from Empress and others.