Pattie: Different Colors Every Session

I have a bit of an issue with different colors being used for the background with every session.

The wood of this shelving unit that is behind Pattie is not as uniform as I would like. Each space currently has slightly different colors. Of course there are some slightly different shades throughout each space in the photo but I think my current painting is too far off. I need to establish a method for reproducing a similar color for these shadowed areas then working from there every session as to unify them better.

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