That is an issue, even for experienced writers occasionally. Best bet is to educate your teachers. Show them what you do not want them to do.
1. Create a presentation that has examples of what you do not want to see
2. Convert the presentation to a video, e.g new versions of PowerPoint can convert presentations to a wmv file.
3. If needed Convert wmv file to mp4 and put it into the Moodle - Handbrake will easily convert most formats.
5. Make your presentation at a staff meeting, so everyone gets the message, and your mp4 file is uploaded to a Staff only course on what to do, how to use the new editor.
6. Trust your teachers to mostly get it right, and those few who get it wrong, well, they can be reeducated but it can take a few tries.
Colour is always an issue, so talk about the colour wheel, and talk about opposites offering high contrast, which is what text should always be.
Too much colour overwhelms the message
Too little colour makes it boring and detracts from the message
So the message is keep colours to a minimum, but keep them simple.
One issue that is a lot more common than we think is background colour. If background colour is too light there is a risk of luminosity overwhelming the text and the message is lost. Some younger people are subject to serious problems with Irlen's Syndrome where luminosity is preventing them of following the text. They need a muted pastel colour, a blue often works, but a pastel green can be ok too, with very dark text, black on green or navy on pastel blue, not red on green. In Oz, it is an unsettling truth that many Aboriginals have Irlen's and it is rarely diagnosed adequately. It is actually even more common amongst Middle Eastern peoples I have been told. Is also not that uncommon in European and Asian populations either. It is similar to dyslexia, but can have a much deeper impact and the two are often confused.
Colour blindness too is an issue, so red on green and green on red should always be avoided.
Be careful of the "signal colours". Red, yellow and green. Reds and yellows are warning colours, so should really be avoided, muted or pastel greens can be useful in large blocks, are are better used for highlighting a line of text to draw attention to it:
Greens can be used to attract attention to important notes but green text needs to be bold otherwise it is lost on this background.
Brick colour, not red, can also be used to attract attention to a critical point. Again, it has to be in bold to avoid being overwhelmed by the luminosity of the background.
Try these things in a word processing document, see what works what doesn't then use that to build your presentation.
Good luck