RGBA Hexadecimal
RGBA is identical to ARGB except that it's expressed with it's Alpha component as the lowest 8bits. For example 0xFF8000FF as ARGB would be Alpha:100%, Red:50.2%, Green:0%, Blue:100% a bright purple. Whereas the RGBA hexadecimal interpretation would be Red:100%, Green:50.2%, Blue:0% and Alpha:100%, a bright orange. It should be noted that RGBA is relatively obscure compared to ARGB. Confusing the two can lead to serious color rendering errors.
Fig.2 - RGBA byte order
ARGB encoding is generally preferable to RGBA encoding, due to the RGB bits remaining in place. While RGBA requires bit shifting changes for all channels. This is a relatively trivial parsing issue, however.
Read more about this topic: RGBA Color Space