Spray the bundt pan (somewhat) generously with oil, not too much but make sure the entire pan is coated. Set a side. Label all the jello packets (trust me, you do not want to skip this step). Set aside.
Place 2 - 4 rows of bowls and decide which order of colors you are doing. As you can see I have 5 colors on the side of the bowl but for now we are only working with 4 colors, save the 5th for a little later (that will be your final layer of jello). It took me a little bit to decide which colors I wanted where. Your first color is the last set of bowls.
From here, I'll refer to the bowls as row 1 and row 2. Measure out 1/3 cup of jello (each color gets its own bowl) in row 1 and add the rest of the jello to the bowl in row 2, make sure each set of bowls are the same color jello (bowl one in row 1 and bowl one in row 2 are the same color and so on).
Add 2 tsp of gelatin to each bowl in row 1 and 1 tsp of gelatin to each bowl in row 2. Add 1/4 can of the condensed milk to each bowl in row 1, about 5-6 tbsp (it's hard to measure condensed milk precisely).
Add 1 cup of boiling water to each bowl. Mix really well until all the gelatin dissolves. If you feel like some of the gelatin is not dissolving, pop the bowl into the microwave for 30 seconds, I only had to do this with a few bowls. Rinse the whisk between each color.
Starting with the last set of bowls (this will be your top color once the bundt pan is flipped unto a cake stand). Very gently pour the clear jello (row 2) into the greased pan. I usually reserve about 1/3 cup of jello and I do this so the top layer is not too thick. Pour into a small dish and have it as a snack layer. Place in freezer for 10-15 minutes, check with your finger if it's firm. Pour the corresponding color and place back in the freezer. Repeat with all colors.From here the process goes fairly quick. wait about 10 minutes between pouring new layers.
Prepare the final color. Place the jello in a bowl and add 1 cut of boiling water, mix until dissolved. Set aside. I usually do this after the first few layers are firming up.
Allow for the jello to firm completely, at least 5-6 hours but preferably over night.
Very gently pull the jello away from the sides of the pan, don't forget the center. Place a cake stand or a large flat plate over the jello and carefully invert it. The jello should come right out, if it doesn't - fill a large bowl of hot water and submerge the pan for 15-20 seconds. Be very careful not to get water on the jello and not to keep the pan too long in the hot water, otherwise the jello will start melting an you will have a mess on your hands.