You will need:
Plant stems have bundles of tubes inside them called 'vascular bundles'.
When leaves and petals lose water to the air, the water must be replaced.
Eventually the coloured liquid must be pulled through the stems to replace the lost water, colouring the leaf tips and flower petals. This process is 'transpiration'.
Vascular bundles that carry water from the roots to the leaves are called XYLEM. It was those vascular bundles that were transporting the coloured water up the flower stem. Try splitting the stem in middle and placing the 'two stems' in different coloured solutions. Can you make a flower with two colours or more?
Related experiment: celery transpiration