@X-O

The Training Room is above the Mission Room through the ceiling where the green machine protrudes out from.

You get there by Air Hookshotting the Small Platforms just above the Orange Mission Screen on either side to flip up to them or you can Jump off the wall and land on them(I always have Run on).
Standing on them, you can Double Jump up to the walls where the Green machine is and wall-jump the rest of the way.

If you're skillful enough, you can Hookshot the inside edges of the hole and attempt to wall-jump up.

Once you're up there. The right is the Training Room with the Fading Onyx paint. The left is the Boss Rush room where you can earn the Ultimate Blend paint.

Where the heck is the training room?? And how do I get the boss rush?

[down] + [hookshot] to pick up a block. press [attack] or [burst] while holding a block to increase the damage of your next burst technique.

I believe it's down + grab

Do y'all know what the button input is to do the block grab move from Purply Blank/Stained Purple ? I did it by accident once and haven't been able to figure it out again

thanks for the guide! I rushed to get Speedy Teal and I think your description of the effects is a bit of a understatement xD

honestly i kinda wish the paint jobs didn't cripple burst energy gains

awesome

Also, completing either gauntlet will also grant you the Palette Chip.

there's a couple small platforms added in the update that let you reach it