Monitor color has been changed to yellowish.

There are three Cathod Ray guns responsible for the millions of
colors.All colors are produced by mixing the three basic colors namely
Red Green and Blue (RGB) at suitable proportion. If any one of the
three guns fail firing then we get improper colors.
Try
(1) Simply tap on the monitor and see the result.(Keep the monitor on during this trial.)
(2) Disconnect the Monitor.and Slap it at the back by keeping it on a pillow with the screen facing down - it will resolve the problem if the failure is due to the loosening of the Head due to repeated thermal expansion and contraction.
(3) check the signal cable for loose connection, twisting etc on both ends - at the back of the CPU and Monitor (it is fixed) -
(4)tighten the screws at the backside of the CPU

Best of luck

ProfSweetlin

Try un twsiting your signal cable if its twisted. Else your Red And Blue Signals are faulty. or the RGB\Video Board of the CRT has a problem.