The 1881 1d Lilac 16 dots (S.G. 173/K8) is known with the PEARS' SOAP. underprint in outline letters in three colours, orange, mauve and blue. Examples of all three are shown below:
This is very similar to the "Half Penny" underprint on the 1/2d Vermilion.
This stamp usually has a pinhole which, according to Stanley Gibbons, was introduced when the stamp was pinned prior to underprinting. This seems rather unlikely to me as the pinhole in the above stamp is actually through the serif at the foot of the "n" of the "One" and appears to post date the underprinting.