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The purpose of drafting film is not to color
The purpose of drafting film is to do super fine and precise detail renders over rougher, construction drawings.
Imagine you have a heavily structured drawing with loads of vanishing points and other constructions lines you don't want to show through your final design
So you whip out a sheet of this to go over and do a high quality clean render with all the bevels and details that would not read with all the construction lines.

You can use base colors on the back and then put another layer of color on the front for a richer more opaque look. My favorite thing is using a pencil eraser for the highlights instead of working around them. It removes color completely and very easily. Then you put your highlight color down. Sweet! Not my primary go to but a fun option definitely.

If you want to use colored pencil over marker for more vibrancy, apply the marker to the backside of the film, then turn over and apply the pencil. Because drafting film is semi transparent, you can easily work both sides to achieve more depth of color. I have not used this particular brand, but a good quality film should accept 6 to 8 layers of colored pencil.  It does require planning and choosing your colors carefully.

Yes, Polydraw can be drawn (or painted) on, though this was primarily intended to be a much tougher replacement for tracing paper, which is why toughness and dimensional stability (doesn't wrinkle) is highlighted. Tracing paper wrinkles at the slightest hint, even the warmth of your hand resting on it. Polydraw is untearable will hold its shape on any scale, you can be even wash it in soap and water (or solvents) and re-use it. I use it to transfer oil underdrawings to canvas on the 1M scale. If you want to trace a huge image this is the stuff to use, tracing paper won't work on that scale.

You can use more layers but you must layer very thin.  You put on the pencil way to hard. You can't use drafting film like normal paper. It's a different technique.

Dura-Lar Graffix 0.005 is best to use. Great for pastel pencils too.

У нас это называется калька. Преподаватель старой военной школы на одном месте мог срезать изображение туши семь раз..

I don't think i've ever been that invested in seeing a marker just... not smudge lol very well put together video! full disclosure, i have no experience with drafting anything - ever, but i would assume the translucence, lack of tooth, and erasable-ness are the main points of using this film. you can backlight the work effectively for clarity and mistakes are neatly hidden to produce a clean final product, which seems important relative to what i do know of drafting? seems like the ability to cleanly trace existing work is a huge plus, but the color depth definitely suffers (as you pointed out). maybe it's good for examples with less intense palettes like matte colors? either way i enjoyed the experiment!

Fine light layers work - use the back for your underdrawing/basic values - no it won't work if you're into laying down tons of heavy layers, thats not what it's for. It works great for me, I can't use pencils on normal paper, it hurts my wrists (I have Ehlers Danlos) to apply the necessary pressure - (and I moved to pastels because of this) but drafting film allows me to use a very light hand yet still build up layers. Great stuff (expensive stuff) but won't work with every artists technique/style.

Turn it over and put more layers on the back 😊

put a piece of blue paper behind it, see what happens

I must be doing something wrong, cause all those mediums that you used smudged for me

So nice ❤ and so beautiful 🎉 drawing 5:44