Topic title. Basically, what is the Perception check DC for seeing the bead created by Delayed Blast Fireball? If you automatically see it, that kinda makes the spell pointless. Still...
A sorcerer in my game just cast Time Stop and plunked down two Delayed Blast Fireballs. Obviously, the party spellcasters didn't see the spell being cast. If they're not specifically looking for the Delayed Blast Fireball beads, do they even have a chance to see them? For the record, the sorcerer cast two Quickened Hungry Pit spells during the Time Stop rounds as well, so the group is scrambling not to get killed. Lots of stuff going on. I'm not sure how to rule this.
I would think EvilMinion's DC of 20 is pretty accurate.
Though just noticing the bead by no means renders the spell useless. Non-magic characters probably aren't going to know what the hell it is. I would make players also make a spellcraft check at the normal DC for identifying a spell as it is being cast, to know just what the tiny bead is.
If PC's get used to the little beads and you rule they don't need the spellcraft checks a good way to mess with them is to have little red beads hung by fishing line. It''ll make em nice and paranoid.
Unfrotunately as it's glowing it's going to be pretty easy to spot. I would rule 0 in daylight (equivalent to spotting a person) or -10 in dark conditions (equivalent to a battle or stinking garbage) as it's ability to attract the eye is much much greater than it's size. Perception modifiers which haven't already been taken into account (favourable/unfavourable) would then be applied to that
If the delayed fireball was covered with something lightproof (how about putting them in small pouches) then they would be much much harder to spot; +16 for fine sized objects before perception modifiers.