each thread in the warp crosses each thread in the weft at right angles. where a thread in the warp crosses a thread of the same colour in the weft they produce a solid colour on the tartan, while a thread crossing another of a different colour produces an equal mixture of the two colours. thus, a set of two base colours produces three different colours including one mixture. the total number of colours, including mixtures, increases quadratically with the number of base colours so a set of six base colours produces fifteen mixtures and a total of twenty-one different colours. this means that the more stripes and colours used, the more blurred and subdued the tartan's pattern becomes.