Remove gray color in help output

[yubiuser]

What does this PR aim to accomplish?:

PR #1501 added a colorful output for pihole-FTL -h.
For some items it uses a gray color - but this is hardly readable when the terminal background is not pitch black.

This PR removed the gray and switches colors of those items to purple

---

By submitting this pull request, I confirm the following:

1. I have read and understood the contributors guide, as well as this entire template. I understand which branch to base my commits and Pull Requests against.
2. I have commented my proposed changes within the code and I have tested my changes.
3. I am willing to help maintain this change if there are issues with it later.
4. It is compatible with the EUPL 1.2 license
5. I have squashed any insignificant commits. (git rebase)
6. I have checked that another pull request for this purpose does not exist.
7. I have considered, and confirmed that this submission will be valuable to others.
8. I accept that this submission may not be used, and the pull request closed at the will of the maintainer.
9. I give this submission freely, and claim no ownership to its content.

---

• I have read the above and my PR is ready for review. Check this box to confirm

[dschaper]

I have no opinion on this PR directly but in general grey is fine to use, the visibility depends on your terminal color scheme.

[yubiuser]

Sure it depends on the terminal's color scheme. I did not modify this, this is the standard Linux Mint terminal with default settings.

[rdwebdesign]

Accessing via Putty (using default colors), the background is completely black, but the "normal white" is gray.
Only bold white text is really white.

The gray parameters (-q and [-h]) look too dark:

[DL6ER]

I agree on (a) that color schemas are subjective and user-configurable, however, also on (b) that it should look reasonable on default palettes. As both, Putty and Linux Mint can be considered widespread, this change seems to be a good one.

And @yubiuser made sure we do not use it again by deleting the definition of gray altogether 👍

[pralor-bot]

This pull request has been mentioned on Pi-hole Userspace. There might be relevant details there:

https://discourse.pi-hole.net/t/pi-hole-ftl-v5-20-1-web-v5-18-1-and-core-v5-15-released/60495/1