I cannot answer fully for Nifflas, but I can at least say that the smileys and logos on Niff-related pages haven't fully been Nifflas' personal choice. Some of them age back to when WadF was quite new, but time has gone on and things have changed since then.
Specifically the smilies, their look was pretty much decided on non-Niff quarters, mostly because it'd be the most recognisable colour/shape from Niffgames, not to mention the most suitable for smilies.
As not only WaDF has had purple balls, his two 'break-through' games (#modarchive story and #mas2:Operator Status) mainly featured
Purple Ball as the protagonist.
Basically, just the first question is related to something with Niff's own decision on them. I'm sure he'll answer on that as soon as he can.