What's the difference between istihadha and Haydh?

During the last days of my period the discharge becomes very little and the color becomed lighter every day. It goes from dark brown to light brown/dark yellow. All of it occurs within the 10 days period.

I would like to know if it's considered istihadha or haydh? I'm not sure because the discharge becomes very little and light in color.

Menstrual discharge (Hayz) is a kind of blood which is normally discharged every month from the womb of women for a few days. When menses is discharged the woman is called 'Haaez'.

Menses is usually thick and warm and its colour is either black or red. It is discharged with a pressure and a little irritation.

The blood seen by women after the age of 60 years is not classified as Hayz. And as per recommended precaution, women who are not from the clan of Quraish, if they see blood between the age of 50 and 60 years, having the same signs as those of Hayz, they should combine the 'dos' of mustahaza and 'don'ts' of Haaez.

Blood seen by a girl who has not yet completed 9 years of her age will not be classified as Hayz.

Istihaza is usually yellowish and cold and is emitted without gush or irritation and is also not thick. It is, however, possible that at times the colour of the blood may be red or dark, and it may also be warm and thick and may be issued with gush and irritation.

There are three kinds of istihaza viz. slight (Qalila), medium (Mutawaassita) and excessive (Kathira). Explanation is given below:
Little blood (Qalila): If the blood remains on the surface of the wool or pad etc., (placed by a woman on her private part) but does not penetrate into it, the istihaza is called qalila.Medium blood (Mutawassita): If the blood penetrates into the cotton (or pad etc.), even partially, but does not soak the cloth tied on the outer side, the istihaza is called mutawassita.Excessive blood (Kathira): If the blood penetrates through the cotton, soaking it and the cloth (etc.) around it, the istihaza is called kathira.
As you described it is with in 10 days if it has the qualities of The Haez then it is consider as Haez and you have to follow the ruling of the woman who is in the state of haez.and if thus period is match to your periods then it is Haez and in last days of the Haez generally discharge is becoming little only see the qualities of same as Haez then Haez otherwise it is istehaza.