The association with NDNs and having "red skin", comes from the northeastern tribes. They did not have red skin, but warriors covered their bodies in red ochre paint. Therefore, many early colonists refered to them as "red men" or "red skins". The earliest recorded example of the term "redskin" is contained in the following quotation from 1699.
Portion of a letter written in 1699 by Rev. Henry Smith's son, Samuel Smith of Hadley Massachusetts, to his son Ichabod Smith.
Hadley, Massachusetts Colony,
Jan. ye Firste, 1699
My Dear & Dutiful Sonn;
I was of so tender an Age at the Death of my beloved Father, that I am possessed of but little of the Information for which you seek. My Revered Father was an ordained Minister of ye Gospelle, educate at Cambridge in England, & came to ye Land by reason of ye Great Persecution by which ye infamous Archbishop Land and ye Black Tom Tyrante (as Mr. Russell was always wont to call ye Earl of Strafforde) did cause ye reign of his Majestie, Charles ye First, to loose favor in ye sight of ye people of England. My Father & Mother came over in 1636/37, firste to Watertown which is neare Boston & after a yeare or two to Weathersfield on ye great River, where he became ye firste settled Pastor. Concerning of ye earlie days I can remember but little save Hardship. My Parents had broughte both Men Servants & Maid Servants from England, but ye Maids tarried not but till they got Married, ye weh was shortly, for there was great scarcity of Women in ye Colonies. Ye men did abide better. Onne of em had married onne of my Mother's Maids & they did come with us to Weathersfield, to our grate Comforte for some years, untill they had manny littel onnes of theire Owne. I do well remember ye Face & Figure of my Honoured Father. He was as Active as ye Red Skin Men & sinewy. His delights was in sportes of strengthe, & withe his owne Hands he did helpe to reare bothe our owne House & ye Firste Meetinge House of Weathersfield, wherein he preacht yeares too fewe. He was well Featured & Fresh favoured with faire Skin & swete smilinge Mouthe, tho he could frowne stemlie eno' when need was.
Ye firste Meeting House was solid mayde to withstande ye wicked onsaults of ye Red Skins. Its Foundations was laide in ye feare of ye Lord, but its Walls was truly laide in ye feare of ye Indians for many & grate was ye Terrors of em. I do minde me yt alle ye able-bodyed Men did work thereat & ye olde & feeble did watch in turns to espie if any Salvages was in hidinge neare & every Man keept his Musket nighe to his hande. I do not myself remember any of ye attacks mayde by large bodeys of Indians whilst we did remain in Weathersfield, but did oftimes hear of em. Several Families weh did live back a ways from ye River was either Murderdt or Captivated in my Boyhood & we all did live in constant feare of ye like. My Father ever declardt there would not be so much to feare if f ye Red Skins was treated with such mixture of Justice & Authority as they eld understand, but iff he was living now he must see that wee can do naught but fight em & that right heavily.
After ye Red Skins ye grate Terror of our lives at Weathersfield & for many yeares after we had moved to Hadley to live was ye Wolves. Catamounts were bad eno' & so was ye Beares, but it was ye Wolves yt was ye worst. The noyse of theyre howlings was eno to curdle ye bloode of ye stoutest & I have never seen ye man ye did not shiver at ye sounde of a Packe of em. What with ye way wa hated em & ye goode money ye was offered for theyre Heads we do not heare em now so much, but when I do I feel again ye younge Hatred rising in my Blood & it is not a Sin because God mayde em to be hated. My Mother & Sister did each of em Kill more yan one of ye gray Howlers & once my oldest Sister shot a Beare yt came too neare ye House. He was a goode Fatte onne & keept us all in meate for a god while. I guess onne of her Daughters has got ye skinne, as most of ye Weathersfield Settlers did come afoat throu ye Wilderness & brought with em such Things only as they did most neede at ye firste, ye other Things was sent round from Boston in Vessels to come up ye River to us. Some of ye Shippes did come safe to Weathersfield, but many was lost in a grate storm. Amongst em was onne weh held alle our Beste Things. A goode many Yeares later, long after my Father had died of ye grate Fever & my Mother had married Mr. Russell & moved to Hadley it was found that some of our Things had been saved & keept in ye Fort wch is by ye River's Mouthe, [Saybrook] & they was brought to us. Most of em was spoilt with Sea Water & Mould, especially ye Bookes & ye Plate. Of this there was no grate store, only ye Tankard, weh I have, and some Spoones, divided among my Sisters weh was alle so black it was long before any could come to its owne colour agen."
[The remainder of the letter was burnt in a house fire.]
Hope this helps.