Abstract: A post spacer (25) for a liquid crystal cell (26) is formed using colour filter material. At least a portion (15a) of the post spacer (25) and a corresponding pixel colour filter (15b) are defined from a layer of colour filter material (15) using photolithography, in which a photomask (8) comprising a pattern of transparent, half-tone and opaque regions is used to define structures with two different thicknesses t1, t2 simultaneously. The use of a half-tone photomask (8) allows the thickness of the post spacer portion (15a), and, therefore, the eventual height of the post spacer (25), to be defined independently of the thickness of the colour filter (15b). The post spacer (25) may be formed using half-tone photomasks (8) to define more than one layer of colour filter material (15, 23), allowing the ratio t1/t2 to remain within a predetermined limit. The post spacers (25) are preferably located away from thin film transistors (TFTs) (31) and at intersections of row and column electrodes (32, 33).