The first row the sum will be equal to 75.
Now in the third column the missing number(yellow block) will be 75 - (22 + 24) = 29
Now in the middle row the missing number(red block) will be 75 - (21 + 29) = 25
Now in the third row the missing number(green block) will be 75 - (27 + 25) = 23
So the color block having the greatest value is yellow = 29.