Same plant but two different distinct colours. All other blooms on the same plant were the correct colour.
This was an example of one plant of BETTTY DALE, an Exhibition viola taken on 19th June 2013.
The weather had not been very hot whilst the bloom was opening.
Other plants growing in the same patio pot were the correct colour which is the light blue,
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- dscf5065
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- dscf5066
FLORIST PANSY & VIOLA 
these things happen sometimes
possible throw back to original parent plants try and find out both parents used