I think you could use TabHost.TabSpec.setIndicator (view android.view.View) , passing TextViewcustomized (colored) according to your needs.
However, I am re-reading your post again - perhaps you mean how to change the color of the contents of the tab, while I am talking about the tab tab ... If so, sorry, please ignore this answer.
UPDATE
The most convenient way to do this in your xml layout is:
<?xml version="1.0" encoding="utf-8"?>
<TabHost xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@android:id/tabhost"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<LinearLayout
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<TabWidget
android:id="@android:id/tabs"
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
<FrameLayout
android:id="@android:id/tabcontent"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<TextView
android:id="@+id/textview1"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:text="this is a tab - RED"
android:textColor="#FF0000" />
<TextView
android:id="@+id/textview2"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:text="this is another tab - GREEN"
android:textColor="#00FF00" />
<TextView
android:id="@+id/textview3"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:text="this is a third tab - BLUE"
android:textColor="#0000FF" />
</FrameLayout>
</LinearLayout>
</TabHost>