- he scouts your natural with observer
- he immediately goes for colossus timing and doesn't care for your blink stalkers
You say you would try to delay his timing push with harassing, but what if he just pushes with colossus and doesn't matter your blink stalkers?
I can't find unique colossus 1 base timing, but can you still defend when it comes with current units you have?
Around 8 minutes you have 8 stalkers and 1 zealot with this build. When is unique 1 base colossus timing push?