  There is now an increasing number of evidence supporting the idea that the
cosmic Gamma-ray Bursts (GRBs) originate from the collapse of massive stars in
distant star-forming galaxies. Because GRBs are likely detectable up to very
high redshift, and because the gamma-rays are not attenuated by intervening
columns of gas and dust, these phenomena thus offer a unique perspective to
probe the star formation in the early Universe independently of the biases
associated with dust extinction. We report on the R-K colors of the GRB host
galaxies. We find that they are very blue sources, with colors comparable to
those of the faint blue star-forming galaxies at high redshift.
