The answer to this question is hidden in the picture:
During production, the originally white silicone catheters are "marinated", i.e. professionally inserted, in a mixture of clindamycin hydrochloride and rifampicin. Through physical processes the structure of the silicone is opened, the antibiotics introduced and then the catheter is dried. The culprit for the orange color is the color-intensive rifampicin. This is how white becomes orange.

So much for the simple explanation. Here is the chemical one: While clindamycin is white and thus inconspicuous, rifampicin has molecular structures that interact with light and thus produce a color impression. The reason for the orange-red coloration of rifampicin is the absorption properties of its molecular structures: light in the green-yellow spectrum is absorbed, "swallowed", and emitted, reflected, in the red-orange spectrum.

The catheter itself is therefore not orange at all, or at least not as bright orange as it appears. The impression is created by the reflected light of the rifampicin. To the human eye it looks orange, but physically or chemically it is not. In the infrared range, it would probably look more violet-brownish. We simply cannot perceive the absorbed radiation spectrum. That is virtually extinguished and we only see the remaining orange light reflected back.

By the way, this special absorption spectrum of rifampicin is advantageous for the analytics in our quality assurance processes, because it makes it easy to detect!