The colour of the trains doesn't really matter. The calling pattern does, but until TRU (and NPR) are complete, the only way to deliver a 2tph service at the local stations between Manchester and Huddersfield is to add the calls into one of the 'express' services.
Unfortunately whether that express is a Hull or Scarborough service, someone is going to complain. But I would argue Scarborough is probably the 'least worst' as SCA-MAN is a smaller flow than HUL-MAN. It'll also be good to have 2tph direct from Piccadilly to York, albeit they are unlikely to be particularly clockface.
Gatley is a separate issue, but suffice it to say the train would take that length of time to get to Manchester Airport one way or the other, so it may as well call and improve local connectivity.
To be fair none of this is particularly difficult to solve from a schedule perspective. For example:
Scarborough - Blackpool North via Burnley Manchester Road
Saltburn - Manchester Airport via Manchester Oxford Road
Newcastle - Liverpool Lime Street via Manchester Victoria
Hull - Liverpool Lime Street via Manchester Victoria
Leeds - Manchester Piccadilly stopping service
Huddersfield - Manchester Piccadilly stopping service
That would show a connectivity benefit, a reliability benefit and deliver 2tph all day at the stations between Stalybridge and Huddersfield.
The trouble is that current rolling stock, although there's arguably rather too much of it, simply cannot be rearranged to make something like that work.
It would also have some negative capacity implications and journey time implications in that no trains would be able to skip Dewsbury any longer. But still.
