coccus or spherical
Found in soil and water; isolated from the hospital environment and human skin.
The easiest way to differentiate them is by color. Both are pigment producing, and while M. luteus has yellow colonies, M. roseus has pink colonies. If you need a more scientifically valid way of differentiating them, try using a nitrate reduction test. M. luteus can not reduce nitrate while M. roseus can.
It's all about light. Light has all of the colors in it and those that are not absorbed into the bacteria are reflected. It just so happens that the colors of the light spectrum that are reflected give off a pink color. Look into physics and calculus if you want to go more in depth with that one.