-17.65% is the change from 255 to 210
Calculation steps:
[( 210 - 255 ) ÷ 255] x 100 = -17.65%
Formula
Percentage change = [(210 - 255) / 255] x 100
Subtract the new number by the original number
210 - 255 = -45
-45 ÷ 255 = -0.17647058823529413
-0.17647058823529413 x 100 = -17.65%