-1.57% is the change from 255 to 251
Calculation steps:
[( 251 - 255 ) ÷ 255] x 100 = -1.57%
Formula
Percentage change = [(251 - 255) / 255] x 100
Subtract the new number by the original number
251 - 255 = -4
-4 ÷ 255 = -0.01568627450980392
-0.01568627450980392 x 100 = -1.57%