The OP has an HP Latex 315.
As
Smoke_Jaguar mentioned, check the device compatibility list for your RIP software.
HEX or RGB values are basically useless IMO. RGB values are for monitors / screens (digital mediums). Wide format printing uses the CMYK color space.
Inexpensive standalone spectros won't get you very far. If you're serious about color matching, you'll want a spectro that interfaces with your RIP software because you need to calibrate your media profiles using that spectro (typically an "ICC Profile Wizard" built into your RIP software).
Note: Stock profiles from vinyl manufacturers are usually pretty terrible.
Important: There's no point in color matching if you're not creating custom ICC profiles for each of your films (ICC profiles tell your printer how to interpret / process the data acquired from your spectro). In a nutshell, your RIP software will print out test targets / swatches, and you use the spectro to scan them back into the RIP software. The RIP compares the difference of what it tried to print with what your spectro actually scanned -- then makes adjustments that get your profile more calibrated.. rinse and repeat 1 or 2x depending on your RIP's requirements (it's a semi-automated process, and TBH, a bit of a pain, but necessary) which helps you achieve better color matching across all your materials. You should update profiles for each of your films every 1 to 2 years.
And yes, spectros can be very expensive, but you don't need anything "too" fancy. I wouldn't look at anything less than 1.5-2k. X-Rite is very popular (and certainly one of the more affordable RIP supported spectros on the market). Used ones can be found online, but do your research to make sure you're buying a current model. This is the case for any brand since hardware does get deprecated over time. For example, I've been using this one for years (got it lightly used for about $2.5k), but it was deprecated as of Jan. 2025:
https://xritephoto.com/ph_product_overview.aspx/ph_product_overview.aspx?ID=1947&action=support
While it still seems to work, it's just a matter of time before this thing is basically a paper weight (RIP developer will eventually remove the drivers built into their software).
Hope that helps!