Just to rule out something simple, it looks like you don't have an action currently in that screen shot. To the left of the red triangle for a bonus action there would be a green circle if you had an action, and since you're in turn based mode it means you wouldn't be able to cast any spell.
Fair question! He actually does have an action, but when you hover over a spell or other ability that uses an action, which I'd done to pop up the tooltip, the green circle flashes and my screenshot happened to catch it when it was duller. He can cast any other spell, it's just Chromatic Orb that's affected.
The little ticks are the spells you have had Gale prepare, if you check all of the spells with the tick they are the ones that are also in the prepared section.
Duh! I don't believe I didn't make that connection. In my defense, I picked spells that I intended to use at level up and I thought prepared spells were already indicated by the yellow highlight round their icon ... no, that's a rubbish defense, I'm an idiot
