Full Idea
With a three-value approach, if P is 'blob is pink' and R is 'blob is red', then P&P is indefinite, but P&R is false, and P∨P is indefinite, but P∨R is true. This means the connectives & and ∨ are not truth-functional.
Gist of Idea
Logical connectives cease to be truth-functional if vagueness is treated with three values
Source
Kit Fine (Vagueness, Truth and Logic [1975], 1)
Book Reference
'Vagueness: a Reader', ed/tr. Keefe,R /Smith,P [MIT 1999], p.123
A Reaction
The point is that there could then be no logic in any way classical for vague sentences and three truth values. A powerful point.