Purple Cotyledons?

As the title suggests, so of my cotyledons turned purple. Sprouted on around the 3rd of this month and fed for the first time last night. Thing is it's just my Hashberries. The Bubblelicious alongside it turned yellow instead. Not really worried, just curious more than anything. Any ideas?

sound like a phosphorous deficiency to me, maybe from cold temps. Any pics?

Sorry, no pics. I trimmed them last night. I just figured they were hungry because the exact thing happened to the Bubblelicious in the same conditions. The Bubblelicious was just yellow instead of purple. Just never seen that. Maybe its the strain?