Prepare the baking pan by rubbing a little vegetable oil on the bottom and sides.
Sift a good amount of powdered sugar all over the bottom and sides until fully coated, at least 1/8th of an inch.
In a medium sauce pan attached with a candy thermometer, add .5 cup of cold water, 1.5 cup sugar and 1 cup light corn syrup. Stir well bring to the boil on high. Stir often
Bring the sugar mixture to 240 degrees (soft ball) on a candy thermometer. Watch very carefully so it's exactly 240 degrees. Once it reaches 240, turn heat to low.
In a small bowl, which attachment and whisk on high.
Carefully add in the very hot sugar mix into the mixer while it's whisking.
Beat on high for 10 to 15 minutes until thick, but still able to spread.
Once they are fully done whisking, add in 8 drops of red food coloring and 8 drops of blue. Give it one whisk only.
Then add in a few more drops and leave them, they will spread when you pour the mixture.
Pour the marshmallow mix into the prepared baking pan and smooth with a spatula. If you need more color, add in a few drops of food coloring on the top and marble gently with a knife.
Add a nice layer of powdered sugar onto the top and push the marshmallows into the pan.
Let them sit out, uncovered for 6 to 8 hours!
Use a little powdered sugar on a knife to cut them into large squares. Toast and sandwich between some chocolate cookies. Enjoy!