[Extracting logo from background]

Here's how you can do this more precisely using only the Curves+ plugin by pyrochild.

https://forums.getpaint.net/topic/7291-pyrochild-plugins-2017-12-04/

1. Original Image (Layer 1)
   1. Duplicate to Layer 2
2. Switch to Layer 2
   1. Magic Wand Select (Global, 0% tolerance) background
      1. Delete
   2. Adjustments -> Hue / Saturation
      1. Lightness: -100
   3. Magic Wand Select (Contiguous, 0% tolerance) portions of Layer 2 that are the same color as each other
      1. Switch to Layer 1
      2. Copy
      3. Paste into new Layer 3 (or 4, 5, 6, etc.)
   4. Repeat previous Step 2.3 for each distinct color in Layer 2
3. Switch to Layer 3 (or 4, 5, 6, etc.)
   1. Adjustments -> Black and White
   2. Magic Wand Select (Global, 0% tolerance) background
      1. Delete
   3. Use color picker to select the greyscale color of the portions in Layer 3
   4. Expand Colors -> More
   5. Adjustments -> Curves+ (by pyrochild) -> Advanced
      1. In: Value / Brightness
      2. Out: Alpha)
      3. Invert the Curve, straight diagonal line from top left (0,255) to bottom right (255, 0)
      4. Adjust the curve with a third point to the greyscale value (from the color picker) on the top edge (<value>, 255)
      5. Note: if the original image background wasn't white
         1. You'll probably need to set a fourth point on the bottom edge to the greyscale value of the background (<value>, 0)
   6. Magic Wand Select (Global, 0% tolerance) background
      1. Delete
   7. Adjustments -> Hue / Saturation
      1. Lightness: -100
   8. Switch to Layer 1
      1. Use color picker to select the color of the portions in Layer 3
      2. Expand Colors -> More
   9. Switch back to Layer 3
   10. Adjustments -> Curves+ (by pyrochild) -> RGB
       1. Select Red ONLY, adjust the curve to the R: value on the left edge (0, <red value from color picker>)
       2. Select Green ONLY, adjust the curve to the G: value on the left edge (0, <green value from color picker>)
       3. Select Blue ONLY, adjust the curve to the B: value on the left edge (0, <blue value from color picker>)
4. Repeat  Steps 3.1 to 3.10 for each layer created in step 2.3

Note: If the different colors overlap with each other, you'll need to find a solution to fix the borders at the overlaps (e.g. use lasso select to copy from the original image).