Printing on garment uses a technology called direct-to-garment (also known as DTG). Even with this great and popular technology, there is something which it cannot guarantee.
The colours might look different on a real product than what you see on your screen. There are various factors that influence the final appearance of colours on a printed product.
The same colour value will look a little different on when printed on 100% cotton vs. a fabric blend. Similarly, the same colour value will look different when printed on a light vs. dark coloured garment, etc.