Query polymorphic relation table
SELECT describable_id
FROM table
WHERE (property_id, value) IN ((6, 'Red'), (4, '150'))
GROUP BY describable_id
HAVING COUNT(DISTINCT property_id, value) = 2


For strongly 2 pairs

SELECT DISTINCT t1.describable_id
FROM table t1
JOIN table t2 ON t1.describable_id = t2.describable_id
WHERE t1.property_id = 6
  AND t1.value = 'Red'
  AND t1.property_id = 4
  AND t1.value = '150'


If (property_id, value) is unique (by index!) you may remove DISTINCT from both queries.