Asp.net get posted values from an html form in c# using Request.Form an get array value

<input type=hidden name='field[size][large]' value='40' />
<input type=hidden name='field[size][medium]' value='32' />
<input type=hidden name='field[size][small]' value='12' />

<input type=hidden name='field[color][green]' value='22' />
<input type=hidden name='field[color][blue]' value='30' /> 

l have a form like this how ever l can access values using Reuest.Form.GetValues("");

but what am not quit sure is how to get values like in the form above were the input name for example is field[size][large]

i tried using some example here but am not getting the values if l do a loop on all form values l can see the values such as

    foreach (string key in Request.Form)
                    { 
                        sbError.Append("<br>Key : " + key + "=" + Request.Form[key]);
                        // Do something with (name, value).
// using this will output all form values but l want specifically for field[xxx][xxx] not all
                    }

.it will output the value . my question is how can l get all values in the of the field[xxx][xxx] or loop through them

UPDATE :

am using angular to create the html input values for

field['am-created-by-angular']['created-by-angular']

so getting values based on field and loop through it and get the values .

l don't know values created by the user on client side using angular , but however there will be alphanumeric l simply have to capture values