Period  Result
1        Green
1        Blue
1        Blue
1        Red
1        Blue
1        Blue
1        Blue
2        Green
2        Green
2        Green
2        Blue
2        Red
2        Red

Period  Result  Percentage
1        Blue     72%
1        Green    9%
1        Red      9%
2        Blue     17%
2        Green    50%
2        Red      33%

SELECT t.Period, t.Result, ((COUNT(t.Result) / Cnt) * 100) Percentage
FROM table t
     INNER JOIN (SELECT Period, COUNT(*) Cnt
                 FROM table
                 GROUP BY Period) period_cnt
     ON t.Period = period_cnt.Period
GROUP BY t.Period, t.Result

select period,
       result,
       (count(result) / total_period) * 100 as result_percent
from (
  select period,
         result,
         count(*) over (partition by period) as total_period
  from periods
) as t
group by period, total_period, result
order by period, result;