By using a two-color scheme, we have given a closer scrutiny to the Autler-Townes doublet splitting and ac Stark shift in the 2 + 2-photon ionization spectra of CO Ion A(1)(v’=4)<--X (1) Sigma(+)(v"=0) transition in the presence of another strong laser field, which is resonant with the transition C-1 Sigma(+)(v’=0)<--A (1) Pi(v’=4)P-10 branch. All the observations of ac Stark shift/broadening as a function of the perturbing light frequency and its spatial homogeneity strongly support our previous theoretical interpretation for one-color studies. A qualitative interpretation based on the dressed state theory, which is being quantified, for the Autler-Townes splitting as well as the ac Stark effect has been given. In particular, the magnitude of the Autler-Townes splitting is found to vary with the square root of the perturbing light intensity, in line with the dressed state theory.