Not to waste a perfectly good puzzle

I formulated this puzzle as part of a project I'm working on. However, it turned out that it was, uh, a bit too difficult to include for the audience we're aiming it at - it took someone over 40 minutes to solve with me standing right there helping, so it isn't making it into the actual project. Instead, you guys get to enjoy!

It's a bit cryptic:

shiftbackspace

• It's pretty easy by PSE standards ... Apr 17, 2020 at 20:06
• @Randal'Thor - I specifically said "...too difficult to include for the audience we're aiming it at", which has nothing to do with how difficult it is by Puzzling.SE standards. I was simply giving a bit of background on the puzzle. Apr 18, 2020 at 18:11

knowledge

You solve it by:

solve the sudoku as normal.

Then take each resulting letter in the green boxes, in numerical order, and shift them backward through the alphabet by an amount corresponding to the value of the letter in the left column which matches the color of the number in the top row.
For example, the letter in the first green box is O. It is in column 1, which matches the 'D' in color. So you shift the O back four (the value of D) to become a K. Doing this for each of the 9 letters (OPVXQMMJK) produces KNOWLEDGE.

Knowledge

Lanny found this first, I'm just adding solutions and step by steps for the puzzle.

Step by step (I won't add too many as it's a straightforward sudoku, each step is 10 letters added):

(ignore the colours on the left, copied them wrong originally)

These letters can't go anywhere else, and are easy to place

With more letters, the majority of the top can be filled in now.

It's beginning to take shape now with most rows, columns and boxes almost complete. From here we can solve:

What's next?

The green letters spell out 'OPVXQMMJK'. The corresponding colours for the these letters are 'DBGAEHICF'. Shifting the letters back through the alphabet for the corresponding value of these letters gives 'KNOWLEDGE' (Lanny solved this)