Thanks again for the reply.
I shan't pursue this any further, now that I know that I can't just copy across colour codes from Excel to Access. I've got the colour I want now.
I think Excel uses a much smaller colour palette and probably the &H8 at the start indicates that it is only using the 8 colours mentioned below. It may even be using a smaller integer to store the codes than Access does.
Maybe in 64 bit Excel it is different.