In liquid-ink color graphics printing, true black ink is preferred over composite black wherever possible, but poor print quality results from printing black ink too close to color ink, due to limitations in present ink chemistry. A method of processing color bit-map graphics data in a four-color liquid-ink printing system, so as to maximize use of black ink while maintaining a minimum spacing between black and color inks is disclosed. The input data is stored in CMY bit-map color planes. Preliminarily, data representing composite black is moved from the color planes into a K plane for printing by a true black pen. The data is examined to detect any black ink within the minimum spacing from color ink. The examination is expedited by partitioning the data into blocks, and indicating each block as a color block, a black block, or a white block. These indications are conveniently stored in a color table and a black table, in which each block of data is represented by a single bit. Tests for black adjacent color are conducted at the block level, i.e. in the tables, rather than at the individual bit level. Where a black block is detected adjacent a color block, the spacing violation is corrected by moving the corresponding block of data from the K plane back into the color planes for printing as composite black. After such correction, the data is re-checked to detect any new violation(s) resulting from the correction. The process repeated until no minimum spacing violations are found.