- Add an outline. I thought that the right portion of the sprite was completely missing until I decided to import it into an art tool. Most people use the forum on light mode and can’t see white without outlines.
- The number of shades is a no-no, and tends to be a very common mistake. You’re using 4 shades for each poison color, which is something you never want to do. Take a look at the Centipede Poison below:
If you look closely, you’ll notice that the green liquid only has 3 shades. Also notice that the green liquid has an area of 18 pixels. Think about it: Only three shades for 18 pixels. Now let’s go back to your drawing: The three poisons have volumes of 4 pixels each. 4 shades for 4 pixels. Way too much. I recommend using only 2 shades and having a much higher contrast between them.
- Consider using shades a bit differently. Instead of using slightly different colors for each segment, try using the same color for the entire thing and have bright spots within the lines. I don’t know if that made much sense.
Using those points, I made these two sprites. One consists of a white case with dark colors and dark tube caps, while the other has a black case with neon colors and brighter caps. Remember not to have all of them dark or all of them bright, or else there will be contrast issues.
Creating sprites is something that takes a lot of time and practice. If it’s something you enjoy and seek to improve on, keep at it! 
