Dip the q-tips in yellow color and let them dry completely.
Once dry push the uncoloured parts into the straw, if not add some glue for these two to stick together.
Place cotton round under the straw with q-tip as showed on the picture.
Add some glue to the bottom, now fold one side of the cotton round towards the middle and pinch at the bottom for the glue to set.
Add just a bit more glue and fold the other side towards the bottom and pinch for the glue to set.