The listing is alerting Sprint employees, so they're not thrown off by the new colour version if a customer comes in a store seeking a SIM card. Google hasn't provided an official launch date, but we suspect the company will simply update Google Play on 4 February without making too big an announcement.
We've seen several leaks for the red Nexus 5. Both its box and the back have been shown, looking like the same handset we've come to know, with a new coat of paint on top. Pricing for the red version hasn't been provided, but it will presumably stay consistent with the £299/$299 pricing of the white and black versions available on Google Play.
According to a report from Vietnamese site Vietnamnet, Google also has plans for a yellow version of the Nexus 5. However, we've not seen the yellow version leaked, nor does Thursday's Sprint listing mention it.