Progressive-resolution transmission is of significant practical importance for online image libraries. When combined with reversible image compression, it provides a particularly promising framework which not only contributes to lower storage overhead but also to smaller transmission costs. We propose an efficient lossless compression scheme for RGB color images. It consists of a modified reversible subband transformation which is followed by a reversible color decorrelation technique. Switching the (traditional) order of wavelet and spectral transform offers the opportunity to support progressive resolution transmission of spectrally decorrelated wavelet coefficients without compromising compression performance.