Original sentence: Generally spot color is useful when there are up to three spot colors used, unless it is absolutely neccessary to use four or more spot colors that cannot be reproduced using CMYK inks.Using many spot colors may become expensive because of print fees incurred for running each extra color.a fluorescent or metallic color)
Edited sentence: After that it becomes too expensive.Spot color is useful when there are up to three colors.a fluorescent color)