I believe I have been able to duplicate a situation that has perplexed some players in Sunshine Islands. In my current game, where my Character is a Girl, Elliot is at 10 Hearts and yet he refuses my Blue Feather. I have experienced all four of his Heart Events and have fulfilled all ordinary requirements for marriage. Furthermore, I had obtained his 'personal' Sun Stone as well as Taro's 'Owner/Head of Household' Sun Stone. The other Bachelors at 10 Hearts accept my Blue Feather without hesitation.
Why did Elliot still refuse my offer of marriage? I have not given him many gifts but I have spoken to him daily and did give him sufficient Gifts to receive his Sun Stone. Elliot's Most Favourites tend to be Crops and I had shipped most of my Crops or used them in cooking rather than using them as Gifts.
Even when Elliot reached 10 Hearts, I noticed suddenly that the colour of Elliot's heart remained Orange.
He continued to respond with his Orange Level dialogue which is:
Elliot: How's work on the ranch? If you need help, don't hesitate to ask.
10 Hearts therefore is NOT equivalent to the Heart Level required for a successful proposal. I then tested this by offering the Blue Feather and he responded that:
Elliot: ... I'm sorry. I don't think I'm ready to get married yet.
In fact, I only needed to give him 2 preferred Gifts and his heart then turned deepest red and his dialogue changed. Without giving him any Gifts, it took about a week of daily 'meeting and greeting' as well as accepting his invitation to a Festival to change his heart to deepest red. It therefore is not 10 hearts that determines the dialogue but heart Colour in this instance.
His Red Heart dialogue is:
Elliot: Freya, just seeing your face makes me happy for some reason.
Now, when I gave him the Blue Feather, the Proposal Event triggered.
I had known initially that the Heart Levels displayed on the Relations Page were not precise indicators of actual Heart Level but I had forgotten. It is worth remembering. If you have an Eligible Girl or Bachelor at 10 Hearts but the Heart Colour remains Orange, you need to increase the Point total before you can propose marriage successfully.
Veteran Harvest Moon players will recognise the difference between Orange Heart and Red Heart immediately but players without much experience could be confused into thinking that the Orange Heart is Red. Red Heart is a very deep red colour. In any case, if you continue to experience the Orange Heart Dialogue, you have not reached the point total required to marry the Eligible Girl/Bachelor.