Sony uses 3LCD, so that’s typically due to a bad LCD on the 3LCD prism in the projector - in this case, the blue LCD failed. Unless you can line up an individual blue LCD and adjust it so it’s properly calibrated, you usually need to replace the prism with a pre calibtaed assembly with all 3 LCDs attached. The issue is aligning it on 3LCD systems can be difficult. Depending on your experience level, you’re usually better off replacing the entire prism/light engine with a known good one that you do not need to mess with. The primary issue is you usually need to calibrate the other LCDs to be sure everything lines up. Every panel is slightly different and it's not easy.
In most cases, the cost to repair the projectors when you run into issues with these 3LCD projectors is usually cost. Parts tend to cost significantly more then even used equivalent replacements - with many having fewer verified lamp hours as a bonus.
You run into this same problem with cost on the DLP ones, so this isn’t a 3LCD specific issue. I’ve dealt with this on DLP before, and I replaced the entire projector. Original had 1,224 (now 1,227) hours and the one I bought to replace it only has 454 hours (now 457). I know how to change the DMD, but 454 verifiable hours makes up for the waste of a unit.