Any distinction between UK Visa sticker and UK Entry Clearance sticker?

I previously posted a different question pertaining to my Kazakh wife, visiting here in the UK. Sorry for asking multiple questions.

We are wondering though, why she was issued a yellow "Entry Clearance" sticker in her passport for her current visit to the UK as opposed to a green "visa" like her previous two visits? For context, each of her visits were applied for as Standard Visitor Visas; though her last two visits were only planned for a month, whereas for this one she planned approximately three months. Her previous green visas included both validity periods and "duration of stay" being 180 days. In contrast, her current "Entry Clearance" does not include "duration of stay", merely a validity period of six months. So it seems, to our eyes at least, that they serve the same purpose.

Any reason why she has been given a different vignette of sticker, though? My research tells me that yellow entry clearance stickers are usually given for different, longer stay type visas, but this one is a C coded Visit sticker. I have also seen other cases where people were recently surprised to receive these stickers where they usually received green visa stickers.

I assume that, despite the lack of stipulation on the sticker regarding duration of stay, the validity period allows her to stay for up to six months as usual, making this sticker no different from her previous visas?