I need help with coloring clear Borosilicate glass. How much pigment do I need for about 187 g of glass?

The general rule is: the deeper the colour required, the more pigment to be added. The quantity of pigment also depends on the type of pigment - some are very strong and give a deep shade with very little concentration, and other pigments require a high addition to give a desired shade. You will just have to try and see what results you get. It is impossible to give an exact answer to so general a question.