Why would be chest veins be bluer at certain times then others - with no physical exertion. ?

It may be the light: The factors that will impact on the visibility of veins include: amount of blood flow thru the vein, the blood flow thru the overlying skin often determined by the temperature, as well as the nature of the light - incandescent, fluorescent and sunlight, will impart different depth of lighting to the skin.

Normal finding: I am amazed about how often I have women ask me about the veins on their breast. These are almost always normal findings and normal variations of chest veins. They tend to be more pronounced in fair skinned females and they may be related to hereditary factors, temperature, levels of hydration.Pregnancies can certainly increase these veins also. No treatment is necessary unless for cosmetics.