Corrections to All the "Speculation"
First: "White top" scheme is necessary to keep the interior of the aircraft cool while on the ground. Remember the interior is packed with electronics.
Second: The photo is taken at Majors Field, Greenville, TX-the location of the L-3 Comm RC-135 depot. This has been the RC-135 facility since the first conversions by E-Systems over 40 years ago.
Third: It does rain in Texas but it appears they wet down the ramp to produce a more dramatic photo. L-3 continues the Greenville legend of outstanding photography of all their products. Every delivery of an RC after a maintenance/upgrade is photographed from the edge of the runway just after liftoff on the delivery flight. We even briefed the photographers where the rotate point would be, based on conditions, so they could position for the best shot. Besides, a "wet" ramp is more like the environment in the UK.
The aircraft has the Lincoln shield under the cockpit and the Red Goose on the tail. National markings are missing but will probably be added upon delivery to the RAF. Most foreign-bought aircraft are delivered in US registry, probably for legal reasons.
Fourth: With new conversions from KC-135Rs these aircraft can really be considered new airframes as L-3 has worked everything from airframe inspection, corrosion mitigation, all mission equipment installation, and external airframe mods. All flight testing is done by the USAF detachment and company personnel. Truly an L-3 maintained aircraft, with Boeing doing only the engine mods and basic 135 fleet-wide issues.