Guide
The same #315ee8 can be readable or unreadable. Color format and contrast are different problems.
Converting HEX to RGB does not improve a color. Put that color on a different background, though, and readability can change immediately.
HEX, RGB, and HSL are different ways to write the same color
#315ee8, rgb(49, 94, 232), and the equivalent HSL value can all point to the same rendered color.
HEX is compact for web work, RGB exposes channels directly, and HSL is often easier for human adjustment. Changing notation does not magically improve legibility.
Readability belongs to a foreground/background pair
A text color does not have a useful contrast score by itself. The ratio depends on the background behind it.
A brand color may work well on a dark surface and fail on white, or the reverse. Test the actual pair you plan to ship.
Transparency makes the visible color different from the source color
With RGBA or 8-digit HEX, what you see is the source color blended with whatever sits underneath it.
If transparency is involved, calculate and inspect the final rendered combination rather than judging only the unblended RGB values.
Convert, compare, then look at the real interface
Do not use color alone for error, success, or selection states when another cue can help. Labels, icons, borders, and shape make state easier to understand.
A practical sequence is: convert the format you need, measure foreground/background contrast, then check the real text size and UI state on screen.