To edit colour schemes, you will need:
BGB (to use its VRAM viewer and edit colour palettes in realtime, though the colours won't be saved unless you edit the actual values in the ROM itself with...)
-...a hex editor (HxD is recommended)
First, I would recommend switching on "GBC LCD colors" in BGB via Options (F11) > Graphics, especially if you plan to use your colour schemes on hardware.
Here are the address offsets for the following colour palettes:
AMI: 0x40EC
CRT: 0x4114
CUTE: 0x413C
GRAY: 0x4164
RED: 0x418C
RGB: 0x41B4
Here is a screenshot that corresponds to what values you will be editing in BGB's VRAM viewer (only focus on BG0, BG1, BG2, BG3 & BG4--ignore everything else):
Also, take note that the bytes are swapped. If you forget to swap them when editing the ROM's values, you'll end up with a different colour!
To change the name of the colour schemes, just search for the respective name you want to change in text-string form.
The HTML to 15-bit colour converter in conjunction with Instant Eyedropper (or any kind of colour picker that supports returning values in HTML) may help as well. Unfortunately, it doesn't give you the seperate RGB values, so this is best used with editing the ROM directly and restarting BGB to get results :v
As for fonts, dawsx has already covered that, but the location addresses for the fonts changed in 4.8.0 and upwards (hence why a lot of the fonts on that thread end up glitching LSDJ4.8+). I would also prefer using yy-chr over Tile Layer Pro for editing the tiles if you wish to delve into font hacking as well