HEX Codes in Photoshop VARIABLES

Just for general context:

It's a very common misunderstanding that a hex number defines a color. It sounds computerish and geeky, so people assume some kind of absolute accuracy - and that's why it's commonly used for "brand colors". But that's an illusion.

Hex is just base 16 notation for standard RGB numbers. There's nothing special about hex. #d5703f = 213/112/63, #5e80ae = 94/128/174, and so on. Same thing.

Numbers are undefined until associated with a color space. That's what a color space is; a definition of numbers into specific colors and vice versa.

For RGB, you can often (but not always) assume sRGB IEC61966-2.1. For CMYK, all bets are off and everything is to the wind. About the only assumption you can make is that the color you get isn't exactly the one you intended. There's a myriad of CMYK profiles, each corresponding to a certain print process that may or may not be relevant. There is no universal and generic "CMYK" that is equally valid everywhere.

Look at the hex number and resulting color here:

This isn't a native feature of Photoshop variables.

Even for Illustrator variables, it is complex, as shown by @Silly-V 

https://www.linkedin.com/pulse/illustrator-variable-data-advanced-techniques-recoloring-vasily-hall/?trk=hb_ntf_MEGAPHONE_ARTICLE_POST

You should also be able to use decimal codes, I suppose. Hex codes are just practical because you have RRGGBB. But those hex codes translate to an equivalent decimal code. https://www.checkyourmath.com/convert/color/hexadecimal_decimal.php

It's the same number in a different base. Instead of having base 16 (numbers between 0 and 15 - with 15 being represented as F) you will have numbers in our decimal system (base 10, numbers between 0 and 9).