I'm not really sure how to advise as we hate tack and turn out - a complete minefield and so subjective according to whim of judge. I'm also a bit confused because you mention you've hogged him but left his feathers on so you maybe need to talk to a coloured expert rather than a cob person to see what is appropriate.
However I did used to show a hw cob to a high level (Hoys etc) so I do know about them so I'll explain what I did with him.
We hogged him, trimmed off all his feather, coronet hair etc. Trimmed all his excess whiskers off and made sure his throat was nice and clear as well.
We didn't plait his tail but pulled it so it sat between his cheeks at the top and was banged so it sat around his hocks when he carried it.
He wore plain brown leather double bridle with thick noseband and plain browband - workmanlike. His Saddle was a comfortable brown leather one - more GP than show - and he had a discreet brown numnah you couldn't see under his saddle.
I wore a brownish tweed jacket, cream shirt, red and cream spotted tie, Yellowish/buff coloured jods, black leather boots and I wore spurs (not compulsory).
I carried a show cane - rather than a whip - and wore a bowler although a blue velvet show cap was used when bowlers weren't allowed.
You should wear a hair net but not a button hole.
As I say not sure exactly what people wear for showing coloureds - as opposed to cobs - but I don't think blue.
Good luck and let us know how it all goes - most important thing is to have fun!
PS in showing cobs there are only lw and hw classes - no mw like in hunters.