ester,
Don't worry.My son was also like that when he was 6 months old.He liked 糊仔 rather than 白粥.If you have tried some 糊仔, you will know that 糊仔 taste a bit sweet, that's why they like it.
You can try to add some fish/meat/vegetable into the 白粥, so that the 粥 will taste better.But don't force your baby to eat too much a time, just a little bit everytime.Add a little bit a time if your baby like it.