I figured it out here is how you do it.
You create a standard seekbar in your XML.
<SeekBar
android:id="@+id/seekbar_font"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_margin="10px"
android:layout_below="@id/color_font_text"
android:max="100"
android:progress="50"></SeekBar>
Then you customize the seekbar in your onCreate() by creating a boxShape and then force a LinearGradient inside it.
LinearGradient test = new LinearGradient(0.f, 0.f, 300.f, 0.0f,
new int[] { 0xFF000000, 0xFF0000FF, 0xFF00FF00, 0xFF00FFFF,
0xFFFF0000, 0xFFFF00FF, 0xFFFFFF00, 0xFFFFFFFF},
null, TileMode.CLAMP);
ShapeDrawable shape = new ShapeDrawable(new RectShape());
shape.getPaint().setShader(test);
SeekBar seekBarFont = (SeekBar)findViewById(R.id.seekbar_font);
seekBarFont.setProgressDrawable( (Drawable)shape );
Here is an image of the current code up above SeekBar Color Gradient
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