I am wondering about vowels with approximant sounds. I am talking about a variant of a r colored vowel. An r colored vowel is found in words like earth. But, I want to take this a step further. Is there a such thing as an l colored vowel, and is it possible? I assume it is.
Short answer: yes, but it's not as interesting.
"R-colored vowels" are vowels that have are pronounced more like
[ɝ], which is somewhat similar to
[ɝ] is a very interesting vowel, because it has something weird going on with its third formant—something that's not directly connected to height or frontness (the first two formants), or rounding (affects all formants). I'm not sure if phoneticists have a special name for this third-formant weirdness; it's often just called "R-coloring", because it specifically happens near
[ɹ] in English.
So your question could be phrased as, "does any lateral have any properties that can spread to vowels near it?" And the answer to that is yes:
[ɫ] (the velarized lateral) is somewhat close to a high back vowel, and can cause adjacent vowels to become high and/or back. Compare the pronunciation of English "small" against English "bad"; the vowel in "small" was pulled back by the
[ɫ] in Early Modern English times.
However, these changes already have convenient names: "raising" and "backing". So there's not much reason to refer to them specifically as "L-coloring", the same way we talk about "R-coloring". Similarly, if you wanted, you could refer to vowel nasalization as "N-coloring"—but it already has a name, so there's no need to make a new one.
It would be helpful for clarity to specify the articulatory gesture responsible for the "coloring". R-coloring (for me, at least) consists in dropping the blade of the tongue and retracting the tip of the tongue, making a little cup of the front part of the tongue. In this sense of "coloring", and taking the distinctive L-articularion to be the laterality of the tongue, I think the answer to your question is "No". You can't flavor a vowel by making your tongue lower on one side during its articulation. At least, I have never observed such a thing.
However, there is a way to color a vowel that makes it sound as though it is followed by an [l], even though there is no [l] actually there. In my Midwestern versions of words like "bulk" and "bulb", there is no [l]. There is just a lax [u], but with the tongue pulled back to approximate the uvula. Since syllable-offset [l] is uvularized, this suggests that an [l] is hanging around to cause the tongue retraction (as the conventional spelling with "l" indicates).
"Elk" and "milk" are similar, except the l-like quality is now manifested in an off-glide.
This modification of [l] in some dialects of English is popularly described as "velarization", but I think "uvularization" is more accurate, since velarization also involves raising the tongue body, as well as backing.