BMX - bmx question

well im redoing my bike cause its an older mongoose and i said to my parents(im 14) if were gonna get a seat we should re do the bike. they were all for it so a dapy later we bought spray paint and took it apart the next day. me and my dad are prolly spray paintin it somtime this week but my dad said hes gotta sand blast some chrome parts(he works at the city so hes got those machine there he can use. were gettin a seat, some handle bar grips(prolly ordering some OURY BMX Grips from benscycle.net if our local bike shop dont have any) some new brakes(i think)
ok on to my question. i found a seat for bmx bikes and im wondering if all bmx seats fits all bmx bike. heres a link to the seat
http://ddbicyclesandfitness.com/itemdetails.cfm?LibId=41297

and heres my bike thats actually in pieces(took it apart for paintin)
http://i139.photobucket.com/albums/q319/goombadude3/beforebike.jpg
and heres my rough edit of what the bike will look like(the grey is really white but the background is white so i substituted white with gray)
http://i139.photobucket.com/albums/q319/goombadude3/bikeedit.jpg

Thanks bye!

the yellow seat prolly wont be there i just made it yellow

Use a color simulator. Like this one. http://bmxcolor.justfree.com/ It's the best one I've found yet.

And do a black frame, yellow bars & forks, yellow seat post, and everything else black.

thanks for the site minichamp. but my prefence is brighter colors so i dont want black on there. Its just my prefrence

I forgot that the grey is going to be white too. That should look pretty good I guess.