Doesn't look like there is a built in MATLAB function which takes the RGB vector as input and gives the corresponding long or short name of the color as output. You could see the list of eight predefined colors with their RGB triplet equivalents, short names and longnames in the below documentation link
Also, here is the link to a Blog post on a File Exchange community pick about the conversion between RGB and color names. https://blogs.mathworks.com/pick/2019/04/26/convert-between-rgb-and-color-names/
Hope it helps!
