So red is the LSB because you decided it was the LSB. That is not a by-definition thing.
> Endianness is not a concern because you have to specify the underlying integer type, and bit endianness is not a thing
That’s not actually true. There are formats which process bytes LSB to MSB, and formats which process them MSB to LSB. E.g. git’s offset-encoding, the leading byte is a bitmap of continuation bytes, bit 0 indicates whether byte 7 is present.
Both are perfectly justifiable, one is offset-based, while the other is visualisation-based as bytes are usually represented MSB-first (as binary numbers, essentially).
> but when reading a field only its specified bits are read so unspecified bits doesn't change that result. When writing to a field, the source value is truncated to the field size, so you never end up writing to other bits.
I’m quite confused by “bitfield” do you mean the container field (the one that’s actually defined by the `bitfield` keyword) or the contained sub-fields?