how to modify the combinations table (that made by expand.grid() function) in r?

Question

I made small, reproducible example, but my real data is really huge...and have lots of levels.

roomnumber <- c(1,2,3)

color <- c('red','blue','green')

weight <- c(0.1,0.3,0.5)

data <- expand.grid(roomnumber,color,weight)
names(data) <- c('roomnumber','color','weight')

so, the table is as follows. it contains every combinations.

 roomnumber color weight
1           1   red    0.1
2           2   red    0.1
3           3   red    0.1
4           1  blue    0.1
5           2  blue    0.1
6           3  blue    0.1
7           1 green    0.1
8           2 green    0.1
9           3 green    0.1
10          1   red    0.3
11          2   red    0.3
12          3   red    0.3
13          1  blue    0.3
14          2  blue    0.3
15          3  blue    0.3
16          1 green    0.3
17          2 green    0.3
18          3 green    0.3
19          1   red    0.5
20          2   red    0.5
21          3   red    0.5
22          1  blue    0.5
23          2  blue    0.5
24          3  blue    0.5
25          1 green    0.5
26          2 green    0.5
27          3 green    0.5

however, in this data, I want something more. when the "color" variable is "blue", I want to add more combination

specifically, the weight is either 0.1, 0.3, or 0.5 for this combinations but when the "color" is "blue", I want a weight to be 0.1, 0.3, 0.5 AND 0.7

weight_2 <- c(0.1, 0.3, 0.5, 0.7) 

how do I edit this?

(I can easily do manually with this minimal example, but my real data is so huge that it is hard to do manually)