Due to certain unresolved technical and/or material issues, designs’ colors printed on fabric will not exactly look like those viewed on paper; and especially not those viewed exclusively on a computer screen. one of the reasons comes from color gamut issue. There are some colors in your design that are outside of the color gamut that our printer can not actually produce. Instead, it prints the color that is the closest to it , which may cause printout colors differ from design colors.
On the other hand, textile weaves and nap may dramatically or likely modify the final printed products.
If you are very serious about the colors, you should place orders with Color Matching process(sample stage).