there is no difference in respect to their meaning but they are used in different situation, you'll hear the word "sorkh" more often in literature, poetry, .... as the color of blood, a beautiful flower, the sunset,... but if you want to describe the color of your shirt or your car, you'd rather to use the word "ghrmez"

"ghermez " is more common when you want to say the colour of something we mostly use "sorkh" for a kind of flower and you may see it in poems