In color TV broadcasting standards such as NTSC and PAL, the bandwidths of the chrominance signals are even narrower than those of the luminance signals. Also in digital video standards, the chrominance signals are usually low-pass filtered and sub-sampled to reduce the amount of data. Because of these reasons, the chrominance signals have poor transition characteristics and the slow transition causes blurred color edges. In this paper, a color transient improvement algorithm is proposed by exploiting the high-frequency information of the luminance signal. The high-frequency component extracted from the luminance signal is modified by adaptive gains and added to the low-resolution chrominance signals in the proposed algorithm. The gain is estimated to minimize the l2-norm of the error between the original and the estimated pixel values in a local window. The proposed algorithm naturally improves the transient of the chrominance signal as much as that of the luminance signal without overshoots and undershoots. The experimental results show that the proposed method produces steep and natural color edge transition.