By burning the sulfur, sulfur dioxide gas (SO₂) is formed.
The red coloring in the rose is being reduced and turns white. Therefore, the sulfur dioxide is acting as a bleaching agent as well.

SO₂ + red rose pigment---> SO₄^2- + reduced pigment (white)

Going further: the reduced pigment (white) can be oxidized again by putting the rose in nitrogen dioxide gas. See video below.

reduce pigment (white) + NO₂---> NO + oxidized pigment (red)

Standards

Questioning Script

Prior knowledge & experience:

Root question:

• What is happening to the color of the rose?

Target response:

• Burning sulfur must be bleaching out the color

Common Misconceptions:

• While the rose wilted from the heat produced from the burning sulfur, it did not die yet its color was removed.

Other possible questions:

• What part of the rose started to change color first?
• What type of reaction is taking place?
• What gas is formed when sulfur burns?
• What other bleaching agents do you know?
• What is the function of the watch glass over the beaker?

Procedure

Attach the wire to the stem of the rose

Let it hang from the side of a beaker

Place a small amount of sulfur powder in a crucible

Drop a match into the sulfur

Immediately cover the beaker with a watch glass and place in a fume hood

For best results - keep covered

Safety precautions

The sulfur dioxide produced is a very pungent gas and is also poisonous when inhaled in large doses

This experiment should only be done in a fume hood or outside

References & Links:

Science Inquiry
Discrepant Events
A collection of demonstrations from the 1999 NSTA conference
Video Source