Change you flag in setSpan on Spannable.SPAN_EXCLUSIVE_EXCLUSIVE
spannable.setSpan(new ForegroundColorSpan(Color.GREEN), 0, text.length(), Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
UPDATE
NotificationCompat.Builder builder = new NotificationCompat.Builder(
this).setSmallIcon(R.drawable.ic_launcher);
NotificationCompat.InboxStyle inboxStyle = new NotificationCompat.InboxStyle();
inboxStyle.setBigContentTitle("title");
inboxStyle.setSummaryText("summarytext");
String lineFormatted = "test";
Spannable sb = new SpannableString(lineFormatted);
sb.setSpan(new ForegroundColorSpan(Color.RED), 0, lineFormatted.length(), Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
inboxStyle.addLine(sb);
builder.setStyle(inboxStyle);
builder.setNumber(1);
NotificationManager mNotificationManager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
mNotificationManager.notify(1, builder.build());