[feat] pfe-band default color updated to transparent

[starryeyez024]

Currently if you do not add a pfe-color attribute to the pfe-band, the default background color is var(--pfe-theme--color--surface--base, #dfdfdf).

Should it skip the background color property? That way you can just use it for layout and semantics, and not have to override colors you don't need.

[castastrophe]

@coreyvickery What do you think of a transparent default for the band layout? Do you have an opinion on this?

[coreyvickery]

@castastrophe Is transparent just a white band? I'm okay with having the band transparent if someone can choose their preferred color.

[castastrophe]

@coreyvickery Transparent would be whatever color is behind it. The browser default is white but it would depend on the page it's on.

[coreyvickery]

@castastrophe Let's move forward with transparent.

[castastrophe]

Thanks @coreyvickery! Kendall and I discussed this further and it will constitute a breaking change so we can schedule it for when we do a 2.0 release