Grease an 8x8 pan with vegetable oil or spray. You will need two 8x8 pans, one for each color jello.
In a medium sized bowl add 1/2 cup of boiling water and 3 ounces of one Jell-o mix. Whisk until sugar is fully dissolved. You may need to add this to the microwave for another minute to keep the water temperature up for the sugar to dissolve.
Once the sugar is dissolved fully, add 1-1/2 cup of mini marshmallows. Whisk to cover with Jell-o completely and microwave for 30 seconds. Whisk until the marshmallows are completely dissolved.
Pour into the 8x8 pan and chill in the refrigerator uncovered for a minimum of 1 hour.
Repeat all of the above steps for your second flavor of jello.
To each flavor jello, use a butter knife to loosen and remove from the pan as a full sheet. Roll the sheet tightly on itself in parchment paper. Allow to sit for about 30 minutes to stick to itself. Remove the parchment paper and cut into 1 inch strips.
Store jello roll ups in an air tight container kept in the refrigerator for up to 5 days. Keep chilled when not eating.