The Appaloosa's eyes change the plan
Most fireworks advice is about noise, but for an Appaloosa the light matters as much as the bangs. Horses carrying the leopard spotting pattern can have genuinely poor vision in dim conditions, a quirk of the same patterning that gives the breed its spots. Picture that horse at nightfall: bright flashes against a dark yard, shapes he cannot resolve, and noise he cannot locate. The fix is simple and specific to him. Keep the stable and yard lights on through the evening so his surroundings stay readable between flashes, and move around him with steady light rather than swinging a torch beam into his face, which startles a horse whose low-light vision is already working hard.
Build the stable into a refuge
Bring him in well before the first display is due, while the evening still feels normal. Give him a deep bed with banks up the walls, because a startled horse that scrambles against a wall injures himself on the parts of the stable he hits. Hang a full haynet so he has something absorbing and ordinary to do, top up his water, and leave a radio on at conversation level so the bangs arrive against a background of human sound rather than out of silence. Keep his arrangement as close to his normal night as you can: routine itself is a sedative for a horse, and a familiar box, familiar neighbours and familiar timing tell him nothing about the evening is an emergency.
Companionship and the turned-out option
A horse alone in a stable or a field has only his own nerves for company, so make sure he can see and hear another horse, ideally the companion he is settled with every night. If your Appaloosa lives out and is calmer in the field with his herd than in a box, that can be the kinder choice, but walk the fencing and gates before dark, shut anything that opens toward a road, and take off any rug with damaged straps that could slip and tangle if he gallops. Whichever you choose, decide before the evening starts and do not change the plan halfway through, because moving a horse mid-display means leading him through the worst of it.
Through the evening
Visit and talk to him between displays rather than only appearing when something sounds bad. Watch for the signs that he is not coping: sweating up, pacing the box, weaving, calling repeatedly, or standing rigid and trembling. A horse picking at hay and watching you over the door is managing; a horse injuring himself against the walls needs you to stay with him and, if he truly cannot settle, a call to your vet for advice is the right move. Check water again mid-evening, because stressed horses spill and splash more than they drink.
If he gets out despite everything
The realistic fear on fireworks night is a panicked horse through a fence and onto a road. Leaving a halter on a stabled or turned-out horse is a judgement call, but if there is any chance yours could break out, identification he carries with him matters. Should the worst happen, send an alert through KinsLe's Lost Pet Alert System straight away: nearby members get his description and photograph while the trail is fresh, and a finder who catches him can reach you directly instead of your hearing about a loose spotted horse third-hand an hour later.