ArrayAdapter.java

    @Override
    public View getView(final int position, final View convertView, final ViewGroup parent) {
        View row = convertView;
        if (row == null) {
            LayoutInflater vi = (LayoutInflater) getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            row = vi.inflate(layout, null);
        }

        final TimeEntryRowModel entry = getItem(position);
        if (entry != null) {
            row.setBackgroundColor(getContext().getResources().getColor(ColorUtil.getRandomBlockColor(entry.getProjectName())));

            // handle the comment button
            row.findViewById(R.id.comment).setBackgroundColor(getContext().getResources().getColor(ColorUtil.getRandomDarkBlockColor(entry.getProjectName())));

            // if there is a comment, change image to the dotted text bubble
            if (entry.getEntry().getDescription() != null && !"".equals(entry.getEntry().getDescription())) {
                ((ImageView) row.findViewById(R.id.comment_icon)).setImageResource(R.drawable.comment_on);
            }

            // initialize time entry name and task name
            ((TextView) row.findViewById(R.id.time_entry_name))
                    .setText(String.format("%s [%s]", entry.getProjectName(), entry.getProjectCompanyName()));
            ((TextView) row.findViewById(R.id.time_entry_task))
                    .setText(entry.getTodoName());

            // handle the hours text fields
            ((TextView) row.findViewById(R.id.time_tracking_total_hours))
                    .setText(Integer.toString(NumberFormatUtil.getDoubleIntegerUnits(entry.getEntry().getHours())));
            ((TextView) row.findViewById(R.id.time_tracking_total_hours_fraction))
                    .setText(Integer.toString(NumberFormatUtil.getDoubleDecimalUnits(entry.getEntry().getHours())));
        }
        return row;
    }

block_purple.xml

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:state_pressed="true" android:color="@drawable/block_purple_dark" />
    <item android:color="@drawable/block_purple"/>
</selector>

Right, the solution to having ListView rows change colour based on their state is to just create a selector Drawable instead of a selector Color. Then call row.setBackgroundDrawable instead of row.setBackgroundColor during setup.