Though this is not completely sure, many people think that
Ariana, one of the 4 rocket executives, is Silver's mother.
They both have almost the same hair, and of course, Silver
couldn't have gotton that red hair from Giovanni.
In Gen2, Silver had black eyes, like Giovanni's, but in Gen4,
when Ariana was introduced, Silver's eye color changed to red, in HGSS
opening animation. This was probably a message from GameFreak
showing that Ariana is Silver's mother.