In all the definitions given below, the expression ‘colour’ includes black and white.
(1) solid colour : A yam made from fibres of a single colour.
(2) mixture; ingrain : A yarn made from fibres of two or more colours blended together.
(3) twist : A yarn comprising two single ends of different colours twisted together, the single ends being either solid colours or mixtures.
Note: In woollen spinning a twist yarn is known as a marl yarn
Textile Resource (http://www.textile.org.uk)