Vector Colours

Hi, I am new to this and am struggling with colours for vector graphics.

When I upload my designs the colours are nothing like my design on the computer.

For example my bright red colour (RGB 255,0,0) comes out as orange.

I have tried using Inkscape and Adobe Illustrator, also SVG and AI file types and the results are just the same.

So then I tried actually placing my design on a t-shirt and came across the “Design Colours” buttons and found that it sets the colours of the 3 available layers!

So my question now is; are we really restricted to just those 29 colours when using vector graphics?

I always thought vector graphics were the best option as they scale up/down without loss, but if we are so limited on the colours am I better off just using BMP ?

Thanks in advance and sorry if the answer is somewhere simple that I haven’t found.