Thanks for giving the game a shot despite the confusion!
The slime will push any fruit until it is in contact with a wall. Then, the interaction changes depending on the colors. If a slime is the same color as a fruit, it can move through it. The other mechanic is that the slime can exchange a color with the object it interacts with, but the slime also must always have at least one color while objects are able to lose all their colors, and you can only “hold” one of each color. So a blue slime interacting with a green (yellow + blue) watermelon would only able to RECEIVE yellow from watermelon and will turn green and explode. If you’re an orange (red + yellow) slime interacting with a green watermelon, you can either RECEIVE blue or GIVE red to the watermelon.
I think our intro level not being correctly updated to be… an actual tutorial level probably made it a lot more confusing too – we didn’t mean to introduce pushing in the first level, and the sprites should have been updated to fruits with strong color associations.