Does Color Have Meaning?:
Well, yes and no. In the context of doodling, color is generally that of whichever pen you have to hand, so should generally be ignored. Color symbolism is not universal, so cultural differences must be taken into account. Historically, pigments aquire symbolism due to the value of pigments - The celestial blue in Medieval paintings of the Virgin Mary was chosen not because of innate symbolism but because it was the most precious pigment available at the time (Lapis Lazuli).
What Colors Mean:
Color often have a degree of innate meaning due to visual assosications: sky blue, green plants, red blood, brown earth, yellow sun. Colors also have a 'temperature'. Red, orange and yellow are warm colors, while green, blue, blue-grey and violet are cool.
Red often represents power. It can indicate anger ('seeing red') or a need to impose authority, but is also a seasonal, festive color associated with holly berries and Santa Claus. Looking at red increases the heart rate. In China, red is the color of prosperity and joy.
Blue, Black and Gray:
These are conventional colors, indicating stability and strength. Dark blue is often chosen as a corporate color in the financial sector to indicate security. Sea-green and blue can also have connotations of water and the ocean. Gray is sometimes called 'the color of sorrow'. In some Native American cultures black is the color of the life-giving earth, while in western culture it is usually associated with darkness, evil and death.
Purple may represent sexual frustration or a need to appear unorthodox, and is a favorite color of artists. Historically, purple has represented royalty, and in darker hues suggests magic and mystery.
Brown can suggest the earth and autumn. A preference for brown can indicate a conservative personality, even repression. Of course, in clothing and furnishings that depends on fashion, though trends can indicate the mood of the times.
Green usually regarded as a restful color suggesting well-being, and is favored by well-balanced individuals. This is at odds with some associations, 'green with envy', 'going green' with nausea, and money (due to the 'greenback').