甲基紫（methyl violet），俗称龙胆紫，是一系列同类的有机化合物，是副品红的四、五、六甲基衍生物（副品红碱）的混合物。可作为染料、酸碱指示剂、消毒剂，稀释后可用作外用药品。而不同比例的衍生物混合，可以制作出一系列不同深浅的紫色染料。一般来说，混合物的甲基比例愈多，染料的颜色亦较蓝。这些衍生物的特色如下：

纯净的氯化四甲基副玫瑰苯胺以一种蓝绿色的结晶体出现，熔点在137摄氏度。

甲基紫2B

甲基紫6B

甲基紫10B

Methyl violet is a family of organic compounds that are mainly used as dyes. Depending on the number of attached methyl groups, the color of the dye can be altered. Its main use is as a purple dye for textiles and to give deep violet colors in paint and ink. Methyl violet 10B is also known as crystal violet (and many other names) and has medical uses.