Decide which flower species you want to tint. While making this decision, keep in mind that it is easier to tint some flower species than other. Generally, tinting white coloured flowers with very porous stems is a lot easier. Daisies, Allium and Carnations are perfect examples of easy to tint flower species.
Half fill a glass cup or a vase with water. Purer the water you use, the better it will be because the task of tinting fresh flowers would become easier. Make sure the food colouring you use diffuses in water fairly quickly.
Carefully trim the stems of all the flowers you plan to tint. Use a sharp knife for this purpose. Make sure you trim the stems neatly; avoid bruising or crushing them.
Immerse stems of the flowers in food coloured water and set aside the container overnight. Observe the flowers when you wake up in the morning. You will see that the colour of the flowers is already changing.
For multi coloured flowers, consider cutting 4-5 inches of the stem lengthwise from the base into two equal halves. Place both stem sections in food coloured water of different shades.
If you want to get tips and bases of flower petals in different colours, the best way to accomplish this is to place the stem in different colours over consecutive days.
If you leave the stem immersed in food coloured water for several days, stems and leaves of the flower will also change colour. However, such flowers show streaks very quickly as they are tinted in areas that grow fairly quickly.