Use of the phrase "pink and yellow" as a descriptor for Rose Tyler

The following exchange takes place in the New Who series 2 episode "New Earth":

(Rose finally notices the faces of the nursing staff in their nun-like wimples and habits.)

ROSE: They're cats.

DOCTOR: Now, don't stare. Think what you look like to them, all pink and yellow.

Tennant delivers the line with a gently chiding tone: the Doctor is reminding Rose that she's as much an alien to the cat-nuns as they are to her. It's not intended as a romantic line in any way – yet it's spawned a noticeable trend in Doctor/Rose pairing fic where the Tenth Doctor (or the Ninth Doctor, or the TARDIS, or ...) refers fondly to Rose as "pink and yellow."

Between January 2007 and November 2018, the cutoff point for most of my statistical analysis, authors posted 676 stories featuring the phrase "pink and yellow" either directly or metaphorically referring to Rose. The first story using "pink and yellow" in this way appeared on Teaspoon in 2007. Stories peaked briefly in 2009 (51 stories) before dipping back down in 2010 (24 stories) – but they rose to a dramatic peak of over 278 stories in 2013 and 2014 before beginning another decline.

It's natural in fanfic circles for some phrases to go in and out of fashion, but what could be driving these two sets of peaks, especially since the second, more massive one appeared seven to eight years after Rose's last appearance on the show? I have two theories, one for each of the peaks.

The first peak occurred during an especially fertile time in Doctor/Rose fanfic circles, because Rose Tyler's departure from the show was still recent, and there were plenty of fans who wanted to continue her story. Additionally, Series 4, in which Rose returns (and ultimately departs again with the metacrisis Tenth Doctor), aired between April and July 2008. Doctor/Rose fandom remained active during 2009, the year of specials, during which the Tenth Doctor angsted about love and loss in ways that could easily be construed as not just about Donna, but about Rose as well. This kept Doctor/Rose fandom going on LiveJournal and Teaspoon, but by 2010 – the lowest point on the chart since 2007 (or 2018), Archive of Our Own had launched, providing a new, unmoderated, and quite honestly, easier-to-use posting interface than Teaspoon. 2010 also marks the point where Steven Moffat took over the show, and there's a very vocal contingent of Doctor/Rose fandom who dislike Moffat's work and writing style for a variety of reasons; some of these fans simply stopped watching the show and as a result, writing fic.

The second peak is frankly less explicable to me. My best guess is that because 2013/2014 coincide with the height of Doctor Who fandom in the U.S., the show was simply getting more attention from more potential authors who were eventually finding their way to Teaspoon. It's also a point at which some of the most prolific "pink and yellow" authors were posting on a regular basis, meaning the phrase was being seen by more authors who might then choose to include it in their own work. Finally, Gallifrey One academic symposium co-director Joy Piedmont proposes that anticipation for the Tennant and Piper reunion in the 50th anniversary special could have fueled a resurgence in Ten/Rose stories. They're all plausible theories, and I may need to dive deeper into the stories themselves to see if they provide additional clarity here.