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Yes and no. All lavenders are self-blue, but not all self-blues are lavender. The term "self" in the name of a colour means a uniformly solid coloured bird. Self-black is a solid coloured black bird, and while not usually used, is occasionally used in reference to a solid black polish, as compared with a white crested black polish. Ditto for self-chocolate with polish. For self-blues, the standards calls for a uniformly light blue coloured bird. No lacing, no darker head, hackles, saddle, tail as is present in regular, andalusian blue birds.
A lavender bird without the presence of patterns is self blue, and bred to another unpatterned lavender will always produce self blue offspring: true breeding. However, you can create a bird that meets the self blue standard using the blue gene instead of the lavender gene. But due to the nature of the blue gene, it breeds predictably, but not true. Two self blues created with blue and not lavender will not give 100% self blue offspring, but only 50%. I've never spent any time researching exactly what has to be bred out of or into blues to lighten the darker heads/hackles/etc., so I really can't speak knowledgeably about breeding them, just that they do exist, more commonly in other countries, but in the US some of the self-blue OEGB are built with the blue gene rather than lavender.