We observe that a formula given by S. Negami [Trans. Amer. Math. Soc. 299 (1987), 601-622] for the Tutte polynomial of a k-sum of two graphs generalizes to a colored Tutte polynomial. Consequently an algorithm of A. Andrzejak [Discrete Math. 190 (1998), 39-54] may be directly adapted to compute the colored Tutte polynomial of a graph of bounded treewidth in polynomial time. This result has also been proven by J. A. Makowsky [Discrete Appl. Math. 145 (2005), 276-290], using a di