If reality,as constructivists assert,is a mental construction,how can we discriminate between true and false?

Actually, reality is perception. Like colors, we perceive that they are there so we assume that is our reality...but in fact, everything is colorless unless there is light. So, our reality is created by our perceptions and our perceptions are supported by our reality. But, the reality may be false and the perceptions may be true...If reality,as constructivists assert,is a mental construction,how can we discriminate between true and false?
perception is reality! and we truly discriminate false or true by our perception. There are many mentally correct but rationally incorrect situations in our life. the main question is this: is it real or not' not the true or false!