How can i do a histogram of frecuency?

Hi, i have a problem because i don´t know a lot of Matlab but i have to do some things. I have to get for each matrix color, on a vector, how many pixels (matrix elements) there are of each color from 0 to 255. therefore three vectors will be obtained, and each table has 256 cells, each containing frequency appearance of each value in the array. I have to do sequency and then in parallel and compare the two times. Thanks.