Prior to the first shuttle mission (STS-1), the launch of Columbia, there was a defect detected in the batch of suits NASA was making for the pilots to use.
David Clark Company has pioneered air and space crew protective equipment design, development and manufacture since 1941, with products ranging from anti-G suits to space suits.
The company has provided Standard Full-Pressure Suits worn by pilots of various high-altitude aircraft such as the F-4, F-15, XB-70, HL-10, X-24, U-2, and SR-71 Blackbird.
In the early 1980s efforts to produce a standard single suit capable of being used by both SR-71 and U-2 crews, yielded the S1031C suit, replacing earlier suits on an attrition basis.
‘NASA had to borrow some space suits from the U-2 program for the first shuttle mission,’ says Damien Leimbach, former Avionics Technician at U.S. Air Force (2001-2007), on Quora.
‘The David Clark company builds space suits for NASA, but they also build the iconic yellow pressure suits that the U-2 and SR-71 program uses.

‘The program calls them “pressure suits” since they don’t actually fly to space, but they are essentially the same suits that the David Clark company made for NASA.
‘Prior to the first shuttle mission (STS-1), the launch of Columbia, there was a defect detected in the batch of suits NASA was making for the pilots to use. Since the maiden flight of the shuttle mission was also its first real test flight, there was only two crew, a pair of pilots, for that mission.
‘However the suits were not going to be be fixed in time, so NASA called up Beale AFB and said “Hey, we need to borrow a pair of space suits.”
‘And that’s why the crew pictures from the first shuttle mission show the pilots wearing yellow suits (high visibility to easily see downed pilots) instead of the iconic NASA white.

‘I mean, without the NASA patches, you wouldn’t know these guys weren’t SR-71 or U-2 pilots.’
Leimbach concludes;

‘You can even see the green velcro patches on the thighs where U-2 pilots put their note pads and map boards.’
David Clark Company Model S1034 Pilots Protective Assembly (PPA) began replacing the precursor S1031 in the U-2R in 1996 and continues in service to present day. It has also been adopted for use in the NASA ER-2 and WB-57F platforms.

Photo credit: NASA and U.S. Air Force