This tutorial will show you how to make a flower having gradient colours in illustrator.
Using the Pen tool, make the paths of the flower.
Give a gradient colour to the path.
Choose one of the petals and fill it with a Radial Gradient.
Paint the rest of the petals.
Choose the Multiply mode.
Then make a filament and fill it with a Linear Gradient.
Also choose Multiply in the Transparency palette.
After that, draw an ellipse and give a red or yellow gradient.
This is how it will look.
To create a beautiful effect like this, you can duplicate the flower and lower its Opacity.