Hair dyes

There are many colour dyes available in the market. It is said that using these dyes are haraam because it contains chemicals if they are applied on beard they prevent the hair from getting wet. It is obligatory that the beard should get wet while doing wudhu else our wudhu is invalid. Please clarify? Do these latest dyes cover the hair with a layer like nail polish or they bleach the hair with colour? Even if we use these chemical dyes the hair gets wet and washed while bathing. I fail to understand how only while doing wudhu they don’t get wet and washed? This defies logic and science. Please advise.