Set drawable for DividerItemDecoration

Change the shape to rectangle.

Ex:

<shape xmlns:android="http://schemas.android.com/apk/res/android"
       android:shape="rectangle">
    <size
        android:width="1dp"
        android:height="1dp" />
    <solid android:color="@color/primary" />
</shape>

DividerItemDecoration dividerItemDecoration = new DividerItemDecoration(getContext(),
                LinearLayoutManager.HORIZONTAL);
dividerItemDecoration.setDrawable(getContext().getResources().getDrawable(R.drawable.line_decoration));
        recyclerView.addItemDecoration(dividerItemDecoration);
        DividerItemDecoration dividerItemDecorationVertical = new DividerItemDecoration(getContext(),
                LinearLayoutManager.VERTICAL);

        dividerItemDecorationVertical.setDrawable(getContext().getResources().getDrawable(R.drawable.line_decoration));
        recyclerView.addItemDecoration(dividerItemDecorationVertical);

Solution (Programmatically):

If you just want to change the color for the dividers instead of creating a custom drawable you can use a ColorDrawable:

DividerItemDecoration itemDecoration = new DividerItemDecoration(recyclerView.getContext(), DividerItemDecoration.VERTICAL);
itemDecoration.setDrawable(new ColorDrawable(R.color.greycc));
recyclerView.addItemDecoration(itemDecoration);

If the size matters in addition to colors you can use a GradientDrawwable:

DividerItemDecoration itemDecoration = new DividerItemDecoration(recyclerView.getContext(), DividerItemDecoration.VERTICAL);

GradientDrawable drawable = new GradientDrawable(GradientDrawable.Orientation.BOTTOM_TOP, new int[]{0xfff7f7f7, 0xfff7f7f7});
drawable.setSize(1,1);
itemDecoration.setDrawable(drawable);

recyclerView.addItemDecoration(itemDecoration);

Please note that setting the color values in the array requires a full octet of hex values, otherwise incorrect colors will be shown i.e., 0xFF3E3E3E as opposed to 0X3E3E3E.

If you want to change divider color, you can change it from you AppTheme by adding this line
<item name="android:listDivider">@color/your_color</item>