変わる and 変える: a changed plan and a request to change it
Describe changes in plans, attitudes, and colors, and compare the perspectives of 何が変わったか and 何を変えたか.
Report a changed plan
集合時間が八時に変わりました。 says that the meeting time changed to eight. 変わる, read かわる, presents the changed item as its subject.
都合が悪いので、集合時間を変えてもらえますか。 asks whether the meeting time can be changed because it is inconvenient for the speaker. 変える, read かえる, marks the item to change with を.
What something changed into
秋になると、葉の色が変わります。 says that the color of the leaves changes in autumn. It does not describe someone deliberately changing the color.
文字の色を黒から青に変えました。 means that someone changed the text color from black to blue. から marks the original state and に the new one.
Change and lack of change
何が変わりましたか。 asks what changed; 何を変えましたか。 asks what someone changed. They can concern the same modification from different perspectives.
場所は変わりましたが、予定の内容は変わっていません。 says that the location changed but the planned content did not. Do not extend the first change to the second item.
What is the new color in 文字の色を黒から青に変えました?
Show the answer and why
Blue. 黒から gives the original black color, while 青に gives the resulting blue color.