You CAN lower your CYA by dilution--drain half your pool and refill and your CYA will probably be 50, rather than 100.

But, as for fading your pool, it won't happen when you shock to 25, because your CYA is 100. CYA=Stabilizer works by actually inhibiting Chlorine's action. So, to protect your chlorine for breaking down from UV rays, we add stabilizer. But that means we need higher initial, shock and maintenance levels to get the same effect. It's a two-edged sword.

The correct shocking level for CYA of 100 or more is 25ppm.