if you Google #aa151b it will show you the color.
Boring aside if you aren’t interested in colors:
The standard hex format is 2 digits of hexadecimal (0-F are valid values) arranged in red, green, blue.
So for example, pure red would be #FF0000 (255 red, 0 blue, 0 green). So if you wanted yellow, you go #FFFF00
The hex colors are pretty standard for web design (you can often specify colors in css or HTML just using those codes). There’s other formats for things like print, which often uses CMYK. (Cyan Magenta Yellow, and Key (black))
So Forza uses a completely different format for their color picker inside the tool. When I’m trying to match colors for Forza, I use:
http://chris-hill.co.uk/forzacolour.php
It can use an image and then you can select with the eyedropper to select the color you want to replicate, then it’ll spit it out in the hue/saturation/brightness format that the Forza vinyl editor uses.
Example below:
FYI, if you go to a paint place and use hex codes they’ll look at you like you’re speaking another language. In my experience they have no frame of reference with the hex codes, and instead use a system based on how much of which colors are added to a generally white base.