Fucoxanthin is a carotenoid phytonutrient found in brown algae. 

Fucoxanthin absorbs light primarily in the blue-green to yellow-green part of the visible spectrum.

Some metabolic and nutritional studies carried at Hokkaido University indicate that fucoxanthin promotes fat burning (thermogenesis) within fat cells in white adipose tissue by increasing the expression of thermogenin.

References

Maeda H, Hosokawa M, Sashima T, Funayama K, Miyashita K. Fucoxanthin from edible seaweed, Undaria pinnatifida, shows antiobesity effect through UCP1 expression in white adipose tissues. Biochem Biophys Res Commun. 2005 Jul 1;332(2):392-7. PubMed