How to select a section text in middle of paragraphstyle A and paragraphstyle B？

How about

Pseudo Code

... findPreferences ... = style1

myStyle1Finds = myStory.findText()

... findPreferences ... = style2

myStyle2Finds = myStory.findText()

loop .. i

a = myStyle1Finds.characters[-1].index + 1;

b = myStyle2Finds.characters[0].index - 1;

a bit of checking here to see that b is > a

then something close to

a = myStory.characters.paragraphs[0];

b = myStory.characters.paragraphs[0];

// paragraphs in between are

myStory.paragraphs.itemByRange(a,b).fillColor = "None" (well you might want to pick some other properties and values).

HTH

Trevor